fix: clear stale filters and tables on database/schema switch

[datlechin]

Summary

• Rebuild clean base queries for table tabs on restore, stripping stale filter WHERE clauses that may reference columns from a different schema
• Clear filterStateManager when switching databases/schemas to prevent stale filters from being applied
• Invalidate schema provider cache in loadSchema() so sidebar fetcher doesn't return stale cached tables
• Hoist UI clearing (tabs, tables, toolbar) to top of switchDatabase/switchSchema with Task.yield() so sidebar immediately shows loading state instead of stale tables
• Extract QueryTab.buildBaseTableQuery() to share query-building logic between addTableTab and tab restore

Closes #237

Test plan

• Connect to PostgreSQL with multiple schemas
• Apply a filter on a table, switch schema, verify no error on restore
• Close and reopen app after switching schema with active filter — verify no repeated error
• Switch database/schema and verify sidebar immediately clears (shows loading, not old tables)
• Verify tables load correctly after switch completes
• Test with MySQL, MSSQL, MongoDB, Redis database switching

[chatgpt-codex-connector]

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[chatgpt-codex-connector]

Defer tab/session reset until switch succeeds

switchDatabase now clears UI/session state (toolbarState.databaseName, open tabs, sibling windows, and filter state) before any of the throwing switch operations run. If USE, switchDatabase, switchSchema, or reconnectSession fails, the catch path only shows an error and does not restore prior state, so users can lose their open tabs/windows and see the toolbar pointing at a database that was never actually switched to; this is a regression in failure scenarios and the reset should be moved after success (the same failure pattern is present in switchSchema).

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[chatgpt-codex-connector]

Remove unconditional cache invalidation from loadSchema

Calling invalidateCache() at the start of every loadSchema() introduces a race when schema loads are triggered close together (for example, PostgreSQL switch calls loadSchema() and reconnectSession also emits .databaseDidConnect, whose handler calls coordinator.loadSchema()). If one load is in flight, a second call can clear cachedDriver via invalidateCache() and then return early because isLoading is true, leaving schema tables loaded but column fetches/autocomplete broken until another reload.

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