fix(mcp): resolve saved-but-inactive connections in bridge

[Blankll]

fix + feat: MCP connection resolution and SQL write tool split

What

Four commits on this branch:

1. fix(mcp): resolve saved-but-inactive connections in bridge — mcp_bridge::resolve_connection now reuses capabilities::sql::resolve_adapter, which reads .store.dat in-process and connects, instead of only checking in-memory active connections. Credentials never leave the app; McpPolicy authorization still runs upstream in invoke_with_policy. Error messages from get_connection_id are now actionable.

2. chore: sync Cargo.lock sqlkit version to 0.8.4 — lock was stale at 0.8.1 while Cargo.toml is 0.8.4.

3. fix(mcp): remove get_store_value stub capability — the handler always returned {"value": null} without reading the store; MCP should not expose internal app store data.

4. feat(mcp): split SQL write tools by risk level — sqlkit__execute_query was a single Elevated capability carrying all SQL (INSERT/UPDATE/DELETE/DDL ran with no Destructive gate). Split by statement class:

   • sqlkit__execute_query: read-only (SELECT/SHOW/EXPLAIN) → Safe, parallel_ok=true
   • sqlkit__execute_write: INSERT/UPDATE/MERGE → Elevated
   • sqlkit__execute_delete: DELETE/TRUNCATE → Destructive (Confirm Destructive gate)
   • sqlkit__execute_ddl: CREATE/ALTER/DROP → Destructive

   classify_sql parses with sqlparser (dialect-aware). execute_query rejects write/delete/ddl with actionable guidance to the split tools. New module sql_write.rs shares resolve_adapter/execute_on_adapter from sql.rs.

Why

• MCP clients could only reach connections activated in the current UI session, with misleading errors (Missing connectionId in connection config / Connection not found).
• SQL writes had no Destructive gate — any agent with Elevated access could DELETE/DROP freely.
• get_store_value was a dead stub misleading agents.

Checklist

• cargo check passes
• cargo test --lib passes (317 tests, incl. 10 new sql_write classification tests)
• Real Postgres round-trip verified (BEGIN/CREATE/INSERT/SELECT/ROLLBACK)