ADR-0022 stage 8d: schema cache refresh wiring

New `AppEvent::SchemaCacheRefreshed(SchemaCache)` event +
App handler that stores it on `app.schema_cache`.

Runtime helper `refresh_schema_cache(database, event_tx)`
fetches table / column / relationship names via the
`list_names_for` worker request (added in stage 7) and posts
the assembled cache. Wired into every site that already
posts `TablesRefreshed`:
  - `seed_initial_tables` (initial project load).
  - Project-switch path in `handle_project_switch`.
  - `RebuildSucceeded` path.
  - Post-DDL path (`spawn_command`).
  - Post-replay path.

Result: schema-aware identifier completion (added in 8c)
becomes live — Tab on `show data ` offers the actual table
names from the current project, `drop column from T: ` (or
similar) offers existing columns, etc. The cache stays
fresh across DDL and rebuild without per-keystroke worker
round-trips (one refresh per schema-mutating action is
amortised across many subsequent keystrokes).

Best-effort: a failed `list_names_for` for any individual
slot kind leaves that field empty in the cache rather than
suppressing the whole refresh — partial completion beats
no completion.

Tests: 738 passing, 0 failing, 1 ignored (unchanged
total — this stage is wiring, not new test surface; the
synthetic-cache tests from stage 8c remain the regression
net for the completion logic itself). Clippy clean.

src/event.rs

@@ -69,6 +69,11 @@ pub enum AppEvent {
     },
     /// Refreshed list of tables in the database.
     TablesRefreshed(Vec<String>),
+    /// Refreshed schema lookup cache feeding Tab completion
+    /// for identifier slots (ADR-0022 §9 + stage 8d). Runtime
+    /// posts this alongside `TablesRefreshed` after project
+    /// load and after every successful DDL.
+    SchemaCacheRefreshed(crate::completion::SchemaCache),
     /// A persistence failure occurred (ADR-0015 §8). The
     /// application surfaces a fatal banner and exits cleanly so
     /// the message remains above the shell prompt.