plugins: merge the user Plugins page into per-plugin sidebar pages

The generic per-user #plugins page is gone: a plugin with per-user
settings hosts them in its own web_pages() sidebar page instead
(Telegram's pairing page is new; Honcho's opt-in page already existed).
The admin catalog moves from #plugin-catalog to #plugins (old hash
redirected), and user_config_schema is removed from the Plugin trait,
the API DTOs and both plugins — the my-config endpoint, the
plugin_user_configs store and the update_user_config hook stay, now
driven by each plugin's own page fragment.

CLAUDE.md

@@ -77,7 +77,7 @@ Two rules keep the boundary real, and both are enforced by the compiler:
 - **The core never names a plugin.** A plugin contributes tools through `Plugin::tools(self: Arc<Self>)` — the sibling of `http_router()` — so nothing in the core has to downcast to a concrete type. Naming one would drag every plugin in the tree into the core, including a C build via `plugin-transcribe-whisper-local`.
 - **The core never learns about the process shell.** There is no in-core restart hook — the former `restart` tool and its `tools::restart::set_restart_handler` seam were removed. The only coupling to the supervisor is now the `run.sh` exit-code protocol (exit `255` ⇒ re-exec the same binary by path), a seam no code currently triggers (kept for a future admin-driven restart). The live expression of this principle is `skald_core::boot`, which emits startup lines each shell renders (`src/boot_format.rs` here).
 
-**Plugin visibility & per-user config.** The admin surface is split in two: `#plugin-catalog` (`plugin-catalog.js`) is a status board — one card per plugin with an enable toggle + health dot + a Configure button — and `#plugin-detail?id=<id>` (`plugin-detail.js`) holds the instance-config form + per-user access checklist for one plugin (the plugin counterpart of `connector-detail.js`). The user-facing half is `#plugins` (`plugins-page.js`): granted plugins + their per-user config forms. Enable/disable + instance config + access grants are gated by the `plugin.manage` capability (admin-only by construction). Visibility is **opt-in**: a row in `plugin_access(plugin_id, user_id)` grants a user sight of an enabled plugin (`plugin_id` is bare TEXT, never a FK — a `plugins` row exists only after the first toggle). A plugin with a non-empty `Plugin::user_config_schema()` exposes per-user settings, stored in `plugin_user_configs` (**admin-readable system.db — never secrets**) and applied through the `Plugin::update_user_config` hook, whose default just stores the blob via the `PluginUserConfigApi` on `PluginContext.user_config`. Telegram is the reference impl: the user pastes the bot's pairing code in their Plugins page, the override turns it into a `chat_id → user_id` binding (same write path as the `telegram_pairing` tool) and stores a `{linked, chat_id}` status blob for the UI. Endpoints: admin `GET/PUT /api/plugins[/{id}]` + `GET/PUT /api/plugins/{id}/access`; user `GET /api/plugins/mine` + `PUT /api/plugins/{id}/my-config`.
+**Plugin visibility & per-user config.** The admin surface is `#plugins` (`plugin-catalog.js`), a status board — one card per plugin with an enable toggle + health dot + a Configure button — plus `#plugin-detail?id=<id>` (`plugin-detail.js`), which holds the instance-config form + per-user access checklist for one plugin (the plugin counterpart of `connector-detail.js`). There is **no generic per-user plugin page**: a plugin with per-user settings (Telegram's pairing, Honcho's opt-in) hosts them in its own sidebar page via `Plugin::web_pages()`, like mobile-connector. Enable/disable + instance config + access grants are gated by the `plugin.manage` capability (admin-only by construction). Visibility is **opt-in**: a row in `plugin_access(plugin_id, user_id)` grants a user sight of an enabled plugin (`plugin_id` is bare TEXT, never a FK — a `plugins` row exists only after the first toggle). Per-user values are stored in `plugin_user_configs` (**admin-readable system.db — never secrets**) and applied through the `Plugin::update_user_config` hook, whose default just stores the blob via the `PluginUserConfigApi` on `PluginContext.user_config`. Telegram is the reference impl: its pairing page (a `web_pages()` fragment with no backend of its own) reads the `{linked, chat_id}` status blob from `GET /api/plugins/mine` and submits the code through `PUT /api/plugins/{id}/my-config`; the override turns it into a `chat_id → user_id` binding (same write path as the `telegram_pairing` tool). Endpoints: admin `GET/PUT /api/plugins[/{id}]` + `GET/PUT /api/plugins/{id}/access`; user `GET /api/plugins/mine` + `PUT /api/plugins/{id}/my-config`.
 
 **Plugin HTTP routes & web pages.** Every plugin's `http_router()` mounts at boot under `/api/plugin/<id>/` — **enabled or not**: two shared gates wrap each router (`require_auth`, then `guard::plugin_enabled_gate`, which re-checks the DB flag per request and answers 404 while disabled), so enable/disable serves/stops routes immediately with no restart, and plugin responses carry `Cache-Control: no-cache`. The router contract: cheap and safe to build pre-start, handlers tolerant of the not-running state (resolve runtime state per request through a shared cell, as mobile-connector does). A plugin may also contribute **frontend pages** via `Plugin::web_pages()` (`PluginPage { page_id, title, icon, entry, admin_only, priority }`): `GET /api/plugins/pages` returns the caller's visible pages (admin: all; others: non-`admin_only` pages of granted, enabled plugins) with `entry_url` resolved, and the sidebar renders them as menu entries routed `#plugin/<plugin_id>/<page_id>`. A single `<plugin-page-host>` (`web/components/plugin-page-host.js`) dynamic-imports the fragment ES module the plugin serves from its own router, registers its default-exported HTMLElement class, and mounts it with the `plugin-id` attribute — the fragment talks to its backend only through `/api/plugin/<id>/…` and runs with full session privileges (plugins are trusted: they ship in the binary). The frontend knows nothing about plugin page contents or behavior.
 
@@ -388,8 +388,7 @@ The role editor (`roles-page.js`) sets the default group + an allowed-groups che
 | `approval-rules.js` | `<approval-rules-page>` | Approval rule management |
 | `cron-jobs.js` | `<cron-jobs-page>` | Scheduled job management |
 | `connectors.js` | `<connectors-page>` | MCP Connectors row list (one row per connector): user activate/deactivate + granted globals; admin also gets the **Add connector** dropdown (Marketplace / manual form at `#connectors/new`), per-row removal from the catalog, and the **Sign-in providers** modal (§7/§14/§15) |
-| `plugins-page.js` | `<plugins-page>` | `#plugins` — user half: granted plugins + schema-driven per-user config form |
-| `plugin-catalog.js` | `<plugin-catalog>` | `#plugin-catalog` — admin status board: one card per plugin (enable toggle + health dot + Configure → `#plugin-detail`) |
+| `plugin-catalog.js` | `<plugin-catalog>` | `#plugins` — admin status board: one card per plugin (enable toggle + health dot + Configure → `#plugin-detail`) |
 | `plugin-detail.js` | `<plugin-detail>` | `#plugin-detail?id=<id>` — one plugin's admin page: instance-config form (`config_schema`) + per-user access checklist (plugin twin of `connector-detail.js`) |
 | `plugin-page-host.js` | `<plugin-page-host>` | Host for plugin-contributed pages (`#plugin/<plugin_id>/<page_id>`): dynamic-imports the fragment module, registers its element, mounts it with `plugin-id` |
 | `system-agents.js` | `<system-agents-page>` | `#system-agents` — the caller's own run history for the background system agents (TIC): agent, start, status, duration, counters; row → the run's session |