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

Docs/Tasks.md

@@ -1,51 +1,3 @@
-### Issue #20: MEDIUM - No Correlation ID in Background Tasks
-
-**Where found**: 
-- All task files in `backend/app/tasks/`
-- Background tasks don't propagate correlation ID
-- Can't correlate task logs with triggering request
-
-**Why this is needed**: 
-Troubleshooting becomes hard:
-- Task fails
-- Logs show task name
-- Can't find what triggered it
-
-**Goal**: 
-Track correlation ID through entire request lifecycle including background tasks.
-
-**What to do**:
-1. Use contextvars for correlation ID:
-   ```python
-   from contextvars import ContextVar
-   
-   correlation_id_var: ContextVar[str] = ContextVar('correlation_id', default='bg-task')
-   
-   async def blocklist_import_task(source_id: str, correlation_id: str):
-       token = correlation_id_var.set(correlation_id)
-       try:
-           logger.info(f"Starting import for source {source_id}")
-       finally:
-           correlation_id_var.reset(token)
-   ```
-2. Pass correlation ID to background tasks
-3. Include in structured logs
-4. Create task tracking UI showing correlation ID
-
-**Possible traps and issues**:
-- Correlation ID must flow through all async contexts
-- Need to pass ID when scheduling tasks
-- Multiple nested tasks might have parent/child correlation IDs
-
-**Docs changes needed**:
-- Add observability guide for background tasks
-- Document correlation ID format
-
-**Doc references**:
-- DETAILED_FINDINGS.md - Issue #26 "Missing Correlation ID"
-
----
-
 ### Issue #21: MEDIUM - Missing Database Indexes for Performance
 
 **Where found**: