feat: an hour-precision clock that says so, and a cron tool that names the real timezone

The datetime block claimed second precision it never had. It is built once per
request and a turn can run for minutes, so `17:54:31` is a lie by the time the
model reads it — and the model, having no way to know, wrote cron expressions
from it.

Rounding was already there but configurable (`round_minutes`, shipped at 60)
and justified by the prompt cache. That justification was false: the block is
the LAST system message, after the whole conversation, so the cached prefix is
identical from turn to turn whatever the timestamp says. Rounding buys nothing
for caching today.

So the knob goes and the granularity becomes part of the contract: always
truncated to the hour, stated in words, with a pointer to `date` for the cases
that need the minute. `DatetimeConfig` keeps only `enabled`.

- truncation happens in the DISPLAYED zone, not on the UTC epoch: +05:30 zones
  would otherwise render 20:30 — an hour off and not on an hour boundary, which
  reads as precise again.
- the weekday is spelled out. "next Tuesday" is a far more common ask than the
  minute, and weekday-from-date is exactly the arithmetic models get wrong.

Also fixes a real bug found on the way: `execute_task` told the model, twice,
that cron expressions are evaluated in Europe/London — hardcoded, while
TaskManager uses the configured timezone. On a non-UK box every scheduled job
was written against the wrong clock. The description now names the zone the
scheduler actually uses (`TaskManager::timezone_name`), and the assistant's
AGENT.md stops repeating the literal.

CLAUDE.md: record that the instance is in production. The greenfield licence has
expired — schema changes need a versioning mechanism, and per-user SQLCipher
files mean it cannot be a boot-time sweep.

CLAUDE.md

@@ -16,7 +16,7 @@ The design lives in **`blueprint/project-family.md`**. Read it before any archit
 Load-bearing decisions from that document:
 
 - **Not upstreamable.** Nothing here needs to preserve Skald's schema or be portable back to it.
-- **Greenfield.** No users in production ⇒ **no migrations, no backwards compatibility**. Tables get restructured, renamed and moved freely; the schema collapses into a single clean baseline v1.
+- **~~Greenfield~~ — no longer true. The instance is in production.** There are live users with data we cannot recreate, so the greenfield licence (restructure, rename, wipe, recreate) has expired: **every schema change now needs a versioning mechanism**, and "drop the box and re-run setup" stopped being an acceptable answer. Until that mechanism exists, the only safe change is an additive one through `db::ensure_column` (see the DB section); anything that renames, drops, retypes or moves a column or table is **blocked** on building schema versioning first, not something to do carefully by hand. A user's `{userid}.db` is SQLCipher-encrypted and readable **only while they are logged in**, so a migration cannot be a boot-time sweep over every file — it has to run per user, at unlock, and be idempotent. Design for that when the time comes.
 - **Dual memory**: a private per-user pool plus a shared pool. A user's private space is encrypted so that nobody else — the admin included — can read it *through normal use of the system*. Never claim "mathematically impossible": the honest promise is transparency plus verifiability (§3).
 - **Threat model** (§2): the adversary is the **tempted admin**, who owns the box but does not recompile the binary or dump RAM. Do not design against a forensic attacker.
 - **Roles are data, not enums** (§0.1): a `roles` table binds permission-group, run-context and data-handling attributes. "Children" is a seeded preset row, never a hardcoded type.
@@ -132,7 +132,7 @@ The schema is split into two buckets (§5.1), and the split is the point:
 - **`create_registry_tables`** — instance-wide, readable without any user key: `users`, `roles`, `llm_providers`, `llm_models`, `transcribe_models`, `tts_models`, `image_generate_models`, `plugins`, `plugin_access` + `plugin_user_configs`, `approval_rules`, `tool_permission_groups`, `config`, `known_tools`, `llm_requests`, `mcp_catalog`, `mcp_global_servers` + `mcp_global_access`, `oauth_providers`, `role_capabilities`, `shared_folders` + `shared_folder_members`, `projects` + `project_members`, `supervision`, `system_agent_coverage`. The MCP tables back the Connectors model (§7/§14/§15 — see its own section); `oauth_providers` (accessor `db/oauth_providers.rs`) holds one row per identity provider (Google…) — endpoints + `client_id`/`client_secret` + `redirect_uri`, admin-owned household secrets (§4/§15b), never a per-user token. The last two pairs are junction-backed membership: `shared_folder_members` (accessor `db/shared_folders.rs`) for the on-disk shared folders (§6), `project_members` (accessor `db/project_members.rs`) for projects (see the Projects section) — both let a member be read-only (`can_write`) and both drive the container mount topology + the fs routing. Their FKs are registry→registry (same file), which is allowed — unlike an owner→registry key.
 - **`create_owner_tables`** — one owner's content, **identical schema in every file that has it**: `chat_sessions`, `chat_sessions_stack`, `chat_history`, `chat_llm_tools`, `chat_summaries`, `session_scratchpad`, `session_mcp_grants`, `stack_mcp_grants`, `scheduled_jobs`, `job_runs`, `system_agent_runs`, `system_agent_state`, `mcp_user_servers`, `mcp_events`, `sources`, `secrets`, `llm_request_payloads`, `memory_docs` (+ FTS5 `memory_docs_fts`), `reports`. `mcp_user_servers` (a user's activated per-user connectors) carries `catalog_name` as a **bare `TEXT` snapshot** of `mcp_catalog.name`, never a FK — an owner→registry key would fail every INSERT; for an OAuth connector it also snapshots `oauth_provider` + `deliver_json`, and its `api_key` column holds the refresh token (in the SQLCipher-encrypted file, so no column crypto). Because `memory_docs` is an owner table, one definition backs **private** memory in each `{userid}.db` and **shared** memory in `system.db` (the household owner) — see the memory namespace note below. (`projects`/`project_tickets` were owner tables in the single-user past: projects are shareable now, so `projects` + `project_members` are registry tables and `project_tickets` is gone.)
 
-Schema is greenfield (no migrations, §0), but a purely **additive** column lands on an existing DB in place: `db::ensure_column` runs `ALTER TABLE … ADD COLUMN` and swallows the "duplicate column" error, a no-op on a fresh DB where the `CREATE TABLE` already has the column. Used for the OAuth columns on `mcp_catalog` / `mcp_user_servers` so a dev box need not be wiped for an additive change (a full recreate is still valid).
+**The schema is no longer greenfield** (see the production note at the top): a full recreate is not an option anymore. `db::ensure_column` — `ALTER TABLE … ADD COLUMN` swallowing the "duplicate column" error, a no-op on a fresh DB where the `CREATE TABLE` already carries it — is therefore not a convenience for dev boxes anymore but the **only** change shape that is currently safe, and additive-with-a-default is the shape to design towards. Used for the OAuth columns on `mcp_catalog` / `mcp_user_servers`. Anything destructive waits for real versioning.
 
 **No foreign key in the owner bucket may point at a registry table.** SQLite cannot enforce a key across files, not even through `ATTACH`, and sqlx turns on `PRAGMA foreign_keys`: the `CREATE TABLE` succeeds and every `INSERT` fails. `db::tests::owner_tables_stand_alone_with_foreign_keys_on` enforces this by running the owner schema against a database holding nothing else, then inserting a row into each table. One key crossed and was fixed: `chat_history.model_db_id` (dropped — write-only, and `llm_requests.model_name` already records the model).