tech-debt(knowledge): TimingConstants missing cache TTL constants — embedding and search result caches use magic numbers

[mrveiss]

Problem

autobot-backend/knowledge/memory_graph/query_processor.py (PR #3609) defines:

_EMBEDDING_CACHE_TTL_SECONDS = 3600   # 1 hour
_RESULT_CACHE_TTL_SECONDS = 300        # 5 minutes

No matching constants exist in constants/timing_constants.py (introduced in issue #3549). These were left as local constants because there was no appropriate TimingConstants value to reference. Other files added in the same sprint use TTL_30_DAYS, TTL_24_HOURS, etc., but short-lived L2 cache TTLs (1h, 5min) are not represented.

Fix

Add to constants/timing_constants.py:

TTL_1_HOUR = 3600
TTL_5_MINUTES = 300

Then update query_processor.py (and any other files that hardcode these values) to import from TimingConstants.

Acceptance Criteria

• TTL_1_HOUR and TTL_5_MINUTES added to timing_constants.py
• query_processor.py updated to use the new constants
• Audit for other files using raw 3600 or 300 as TTL values