feat(mcp): Connectors — catalog + global vs per-user runtimes (§7/§14/§15)

Re-architects MCP from one owner table + agent-written registration into an
admin-curated catalog with two runtimes unioned per session, surfaced in the UI
as "Connectors" (mcp/schema stays neutral, §0.1).

Two runtimes behind one seam (§7):
- Global runtime: shared, stateless connectors (web-search, Tavily…) on the
  HOST, connected at boot from mcp_global_servers, access-filtered per user via
  mcp_global_access.
- Per-user runtime: a user's activated connectors run INSIDE their container,
  started at first login from mcp_user_servers and living until restart (§9);
  docker exec -i children die via kill_on_drop when the UserContext drops.
- McpProvider trait (mcp/provider.rs): the session round-loop never learns which
  runtime owns a server. McpManager implements it directly (inert ownerless
  bundle); UserMcpView implements global ∪ user with an accessible_global
  snapshot. Both share McpManager::connect_all; McpServerSpec +
  global_row_spec/user_row_spec turn a DB row into a connectable spec.
- mcp-client: McpServerConfig.launch_in runs a stdio command inside a container
  via docker exec -i (set at runtime, never parsed from config).

Authorization is a capability on the role, not `if role==admin` (§0.1/§14):
role_capabilities table + db/role_capabilities.rs — register_remote and
register_local_from_catalog are self-service (seeded on every new role), while
register_local_script and manage_catalog are admin-only. admin holds every
capability by construction. This removes the agent-facing register_mcp/delete_mcp
tools and the mcp kinds of list_items/toggle_item, closing the §14 RCE vector.

Schema:
- Registry: mcp_catalog (vetted templates — schema only, no live creds),
  mcp_global_servers + mcp_global_access, role_capabilities.
- Owner: mcp_user_servers (per-user activations; api_key encrypted at rest,
  catalog_name a bare TEXT snapshot, never an owner→registry FK).
- Drops the old owner table mcp_servers.

API + UI: src/frontend/api/mcp.rs (admin catalog/global/access + user
available/activate/activated, all capability-gated via require_cap);
web/components/connectors.js (<connectors-page>) renders the user view always
and the admin view for role_id === 'admin'.

Deferred: interactive per-user auth (OAuth callback / QR / SSH elicitation, §15)
— only none/api_key wired; no boot seed of catalog presets; per-(user, session)
MCP grant model still open.

crates/skald-core/src/session/handler/mod.rs

@@ -22,7 +22,7 @@ use crate::events::ServerEvent;
 use core_api::message_meta::MessageMetadata;
 use core_api::user_fs::UserFs;
 use crate::llm::LlmManager;
-use crate::mcp::McpManager;
+use crate::mcp::McpProvider;
 use crate::image_generate::ImageGeneratorManager;
 use crate::memory::MemoryManager;
 use crate::tool_discovery::ToolDiscovery;
@@ -292,7 +292,7 @@ pub struct ChatSessionHandler {
     /// True for short-lived automated sessions (cron, tic).
     pub(super) is_ephemeral:     bool,
     pub(super) tools:            Arc<ToolRegistry>,
-    pub(super) mcp:              Arc<McpManager>,
+    pub(super) mcp:              Arc<dyn McpProvider>,
     /// Records tools offered to the LLM each round so the Security-groups UI can
     /// list/gate dynamically-injected tools (interface/plugin/provider tools).
     pub(super) tool_discovery:   Arc<ToolDiscovery>,
@@ -354,7 +354,7 @@ impl ChatSessionHandler {
         is_interactive:        bool,
         is_ephemeral:          bool,
         tools:                 Arc<ToolRegistry>,
-        mcp:                   Arc<McpManager>,
+        mcp:                   Arc<dyn McpProvider>,
         approval:              Arc<ApprovalManager>,
         clarification:         Arc<ClarificationManager>,
         event_bus:             Arc<ChatEventBus>,