feat(store): config table for instance-global app-config overrides

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

docs/DATABASE.md

@@ -14,6 +14,7 @@ Generated from the live schema via `go run ./cmd/dumpschema` -- do not hand-edit
 - [`kind_assignments`](#kind_assignments)
 - [`sync_state`](#sync_state)
 - [`sync_runs`](#sync_runs)
+- [`config`](#config)
 
 ## `users`
 
@@ -263,6 +264,16 @@ CREATE TABLE sync_runs (
 );
 ```
 
+## `config`
+
+```sql
+CREATE TABLE config (
+    key        TEXT PRIMARY KEY,
+    value      TEXT NOT NULL,
+    updated_at TEXT NOT NULL DEFAULT (datetime('now'))
+);
+```
+
 ## Views
 
 ### `current_kind_assignment`