UN-2813 [FIX] Remove unsupported log_level from structlog.configure

Fix critical bug causing CLI to crash with TypeError on startup.

**Problem:**
structlog.configure() does not accept a `log_level` keyword argument.
Passing it raises TypeError, causing the CLI to fail immediately:
```
TypeError: configure() got an unexpected keyword argument 'log_level'
```

**Root Cause:**
Line 35 in cli/main.py incorrectly passed log_level to structlog.configure:
```python
structlog.configure(
    ...,
    log_level=log_level.upper(),  # ❌ Not a valid parameter
)
```

**Solution:**
1. Added `import logging`
2. Configure log level via standard library before structlog:
   ```python
   logging.basicConfig(level=log_level.upper())
   ```
3. Removed unsupported `log_level` parameter from structlog.configure()

**Impact:**
- ✅ CLI now starts without TypeError
- ✅ Log level control preserved via logging.basicConfig
- ✅ Structured logging configuration intact
- ✅ All CLI commands work correctly

**Testing:**
Before: CLI crashes on any invocation
After: CLI starts and respects --log-level flag

Resolves: CodeRabbit comment #2386596263
Related: #1555

Author: Deepak-Kesavan

task-backend/src/unstract/task_backend/cli/main.py

@@ -1,6 +1,7 @@
 """Main CLI entry point for task backend worker."""
 
 import argparse
+import logging
 import signal
 import sys
 
@@ -15,6 +16,9 @@
 
 def setup_logging(log_level: str = "INFO", structured: bool = True) -> None:
     """Setup structured logging."""
+    # Configure standard logging level first
+    logging.basicConfig(level=log_level.upper())
+
     processors = [
         structlog.stdlib.filter_by_level,
         structlog.stdlib.add_logger_name,
@@ -32,7 +36,6 @@ def setup_logging(log_level: str = "INFO", structured: bool = True) -> None:
         wrapper_class=structlog.stdlib.BoundLogger,
         logger_factory=structlog.stdlib.LoggerFactory(),
         cache_logger_on_first_use=True,
-        log_level=log_level.upper(),
     )