Fix critical bugs in export/import feature (PR #225)

Addressed all 6 bugs identified in code reviews:

CRITICAL FIXES:
1. SessionStore.ts: Fixed concepts filter bug - removed empty params.push()
   that was breaking SQL parameter alignment (line 849)

2. import-memories.ts: Removed worker_port and prompt_counter fields from
   sdk_sessions insert to fix schema mismatch with fresh databases

3. export-memories.ts: Fixed hardcoded port - now reads from settings via
   SettingsDefaultsManager.loadFromFile()

HIGH PRIORITY:
4. export-memories.ts: Added database existence check with clear error
   message before opening database connection

5. export-memories.ts: Fixed variable shadowing - renamed local 'query'
   variable to 'sessionQuery' (line 90)

MEDIUM PRIORITY:
6. export-memories.ts: Improved type safety - added ObservationRecord,
   SdkSessionRecord, SessionSummaryRecord, UserPromptRecord interfaces

All fixes tested and verified:
- Export script successfully exports with project filtering
- Import script works on existing database with duplicate prevention
- Port configuration read from settings.json
- Type safety improvements prevent compile-time errors

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

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

scripts/import-memories.ts

@@ -80,8 +80,8 @@ function importMemories(inputFile: string) {
       INSERT INTO sdk_sessions (
         claude_session_id, sdk_session_id, project, user_prompt,
         started_at, started_at_epoch, completed_at, completed_at_epoch,
-        status, worker_port, prompt_counter
-      ) VALUES (?, ?, ?, ?, ?, ?, ?, ?, ?, ?, ?)
+        status
+      ) VALUES (?, ?, ?, ?, ?, ?, ?, ?, ?)
     `);
 
     const insertSummary = db.prepare(`
@@ -127,9 +127,7 @@ function importMemories(inputFile: string) {
           session.started_at_epoch,
           session.completed_at,
           session.completed_at_epoch,
-          session.status,
-          session.worker_port || null,
-          session.prompt_counter || null
+          session.status
         );
         stats.sessionsImported++;
       }