refactor: improve type safety by removing 'as any' casts

Created database.ts with proper database result types and replaced 38+ 'as any' casts throughout the codebase with proper type annotations.

Changes:
- Created src/types/database.ts with TableColumnInfo, IndexInfo, and database record types
- Fixed all type casts in SessionStore.ts (migrations, query results)
- Fixed type casts in SessionSearch.ts, SettingsManager.ts, SettingsRoutes.ts
- Improved MCP server JSON schema typing

All builds pass and worker service runs successfully.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Sonnet 4.5 <noreply@anthropic.com>

src/services/worker/SettingsManager.ts

@@ -37,7 +37,7 @@ export class SettingsManager {
       for (const row of rows) {
         const key = row.key as keyof ViewerSettings;
         if (key in settings) {
-          (settings as any)[key] = JSON.parse(row.value);
+          settings[key] = JSON.parse(row.value) as ViewerSettings[typeof key];
         }
       }