Add fail2ban DB index management and socket-based path resolution

- New get_fail2ban_db_path() in setup_service resolves DB path from configured socket path
- New ensure_fail2ban_indexes() creates missing performance indexes on bans table
- Call ensure_fail2ban_indexes on every startup before first ban query
- Remove completed tasks from Docs/Tasks.md
- Update Docs/PERFORMANCE.md with index findings

backend/tests/test_utils/test_fail2ban_db_utils.py

@@ -1,6 +1,60 @@
 """Tests for fail2ban_db_utils module."""
 
-from app.utils.fail2ban_db_utils import escape_like
+import sqlite3
+from pathlib import Path
+
+import pytest
+
+from app.utils.fail2ban_db_utils import (
+    ensure_fail2ban_indexes,
+    escape_like,
+)
+
+
+@pytest.fixture
+def tmp_bans_table(tmp_path: Path) -> str:
+    """Create a minimal fail2ban-style database with bans table."""
+    db_path = str(tmp_path / "test_f2b.db")
+    conn = sqlite3.connect(db_path)
+    conn.execute("CREATE TABLE bans (jail, ip, timeofban, bancount, data)")
+    conn.execute("CREATE INDEX idx_jail_timeofban_ip ON bans(jail, timeofban)")
+    conn.execute("CREATE INDEX idx_jail_ip ON bans(jail, ip)")
+    conn.execute("CREATE INDEX idx_ip ON bans(ip)")
+    conn.commit()
+    conn.close()
+    return db_path
+
+
+@pytest.mark.asyncio
+async def test_ensure_fail2ban_indexes_creates_missing_index(tmp_bans_table: str) -> None:
+    """Index is created when idx_bans_timeofban_desc does not exist."""
+    await ensure_fail2ban_indexes(tmp_bans_table)
+
+    conn = sqlite3.connect(tmp_bans_table)
+    conn.row_factory = sqlite3.Row
+    cur = conn.execute(
+        "SELECT name FROM sqlite_master WHERE type='index' AND tbl_name='bans'"
+    )
+    index_names = [str(r["name"]) for r in cur.fetchall()]
+    conn.close()
+
+    assert "idx_bans_timeofban_desc" in index_names
+
+
+@pytest.mark.asyncio
+async def test_ensure_fail2ban_indexes_idempotent(tmp_bans_table: str) -> None:
+    """Calling twice does not raise or duplicate the index."""
+    await ensure_fail2ban_indexes(tmp_bans_table)
+    await ensure_fail2ban_indexes(tmp_bans_table)
+
+    conn = sqlite3.connect(tmp_bans_table)
+    cur = conn.execute(
+        "SELECT name FROM sqlite_master WHERE type='index' AND tbl_name='bans' AND name='idx_bans_timeofban_desc'"
+    )
+    count = len(cur.fetchall())
+    conn.close()
+
+    assert count == 1
 
 
 def test_escape_like_percent_sign() -> None: