Bug: Phase Validation Bypass in EntityAgent Exception Handlers

Exception handlers in `act()` and `observe()` methods call `self.set_phase()` instead of `self._set_phase()`, bypassing phase transition validation.

### Root Cause
Two methods exist for setting phase:
- `_set_phase()` (line 97): ✓ Validates transitions via `check_successor()`
- `set_phase()` (line 266): ✗ Sets phase directly without validation

Exception handlers incorrectly use the public method that skips validation.

### Impact
During error recovery, agent can be forced into invalid phase state, causing:
- Invalid agent state after exception recovery
- Downstream errors from invalid phase transitions
- Race conditions in multi-threaded scenarios

### Current Code (lines 187-191, 209-213)
```python
except Exception:
self.set_phase(entity_component.Phase.READY) # BUG: No validation
raise
```

### Fix
```python
except Exception:
self._set_phase(entity_component.Phase.READY) # Fixed: Validates transition
raise
```

This ensures phase transitions are validated even during error handling.

Start in the act() and observe() exception handlers at lines 187-191 and 209-213, then compare their set_phase() calls with _set_phase() at line 97 and set_phase() at line 266. Update both handlers to preserve phase-transition validation and verify that exception recovery no longer bypasses the documented checks.

Written by the indexing model from the issue text.