fix: preserve search index across server restarts

Remove unconditional DROP TABLE from init_search_index() that was wiping
the FTS5 search index on every MCP server startup.

The bug was introduced in PR #439 (v0.16.3) when splitting SQLite and
Postgres search implementations. The DROP TABLE was added with a comment
about Base.metadata.create_all() potentially creating a regular table,
but this caused all indexed data to be lost whenever Claude Desktop
restarted the MCP server.

Symptoms users experienced:
- Notes searchable immediately after creation
- Search returns empty results after ~30 minutes (server restart)
- Files exist on disk but search index is empty
- recent_activity() shows "No recent activity"

The fix simply removes the DROP TABLE since CREATE_SEARCH_INDEX already
uses "CREATE VIRTUAL TABLE IF NOT EXISTS" which safely handles both
cases (table exists vs doesn't exist).

Affected users should run `basic-memory reset` once after updating to
rebuild their search index.

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

Co-Authored-By: Claude <[email protected]>

Author: phernandez

src/basic_memory/repository/sqlite_search_repository.py

@@ -27,17 +27,15 @@ class SQLiteSearchRepository(SearchRepositoryBase):
     """
 
     async def init_search_index(self):
-        """Create FTS5 virtual table for search.
+        """Create FTS5 virtual table for search if it doesn't exist.
 
-        Note: Drops any existing search_index table first to ensure FTS5 virtual table creation.
-        This is necessary because Base.metadata.create_all() might create a regular table.
+        Uses CREATE VIRTUAL TABLE IF NOT EXISTS to preserve existing indexed data
+        across server restarts.
         """
         logger.info("Initializing SQLite FTS5 search index")
         try:
             async with db.scoped_session(self.session_maker) as session:
-                # Drop any existing regular or virtual table first
-                await session.execute(text("DROP TABLE IF EXISTS search_index"))
-                # Create FTS5 virtual table
+                # Create FTS5 virtual table if it doesn't exist
                 await session.execute(CREATE_SEARCH_INDEX)
                 await session.commit()
         except Exception as e:  # pragma: no cover