Improve: add contextual logging in scheduler exception handlers

[neuromechanist]

Summary

Several scheduler exception handlers log the error but omit key context (community_id, sync_type, failure count) that would be needed for debugging production issues. The pattern of _track_failure() swallowing context in the except block is fine, but surrounding try/except blocks could do better.

Locations

File	Lines	Issue
scheduler.py:104	except Exception as e:	Logs to _track_failure but no explicit log line with community_id
scheduler.py:146	Same pattern	No direct error log with sync context
scheduler.py:220	Same pattern	Missing community context in error log
scheduler.py:279	Same pattern	BEP sync errors lack community_id in log

Current Pattern (deficient)

try:
    ...
except Exception as e:
    _track_failure("github", community_id, e)
    return False  # No explicit error log with community_id

Recommended Pattern

try:
    ...
except Exception as e:
    logger.error("GitHub sync failed for %s: %s", community_id, e)
    _track_failure("github", community_id, e)
    return False

Acceptance Criteria

• All scheduler exception handlers log community_id and sync_type
• Error messages include the underlying exception for debugging
• No silent failures (exceptions swallowed without log output)