Modularize database.svelte.ts into focused managers

[mikenikles]

Summary

Refactors the ~1700-line UseDatabase God Object into 11 focused managers following the separation of concerns principle.

New managers created:

• ConnectionManager - connection lifecycle (add, reconnect, remove, test)
• PersistenceManager - state serialization and persistence
• StateRestorationManager - state hydration on reconnect
• TabOrderingManager - generic tab ordering and removal
• QueryExecutionManager - SQL execution and CRUD operations
• ErdTabManager - ERD tab management

Extended existing managers:

• SchemaTabManager - added table metadata loading
• ExplainTabManager - added execute and result conversion
• QueryTabManager - added focusOrCreate, loadSaved, loadFromHistory

New API structure:

const db = useDatabase();

// State access (read-only)
db.state.activeConnection, db.state.queryTabs, db.state.schemas...

// Manager access
db.connections.add(), .reconnect(), .remove(), .test(), .setActive()
db.queries.execute(), .goToPage(), .updateCell(), .insertRow(), .deleteRow()
db.queryTabs.add(), .remove(), .rename(), .setActive(), .loadSaved()...
db.ui.toggleAI(), .setActiveView()
db.tabs.reorder(), .ordered
db.persistence.flush(), .cleanup()

Test plan

• Verify database connections work (add, reconnect, remove)
• Verify query execution and CRUD operations
• Verify tab management (create, close, reorder, rename)
• Verify persistence across app restarts
• Verify all views render correctly (query, schema, explain, ERD)

🤖 Generated with Claude Code