[BUG] Memory entries duplicate massively on every `apc collect` run — no deduplication

[FZ2000]

Tool Affected

All (cache / collect logic)

What Happened

After multiple runs of apc collect, the local cache contains 203 memory entries despite the source tools having only a handful of actual memory files/entries.

apc memory list shows the same entries repeated dozens of times:

[preference]
  - Docker test pref  (manual_add)
  - Persist across collect  (manual_add)
  - Docker test pref  (manual_add)
  - Persist across collect  (manual_add)
  - Docker test pref  (manual_add)
  ... (20+ duplicates of the same entries)

apc status shows Memory: 203 while only ~10 unique entries exist across all tools.

Root Cause

src/cache.py's merge_memory() function merges new entries into the existing cache, but the deduplication logic appears to fail for manual_add entries and entries that share the same content but were re-extracted across multiple collect runs.

Each time apc collect runs, raw-file entries (e.g., claude-code/CLAUDE.md, openclaw/MEMORY.md) are re-added without checking if an identical entry (same source_tool + source_file) already exists.

What Was Expected

• apc collect should upsert memory entries — update existing ones, not append duplicates
• Entries with the same source_tool + source_file (or same entry_id for manual entries) should never be duplicated

Impact

• LLM memory sync becomes extremely expensive (sending 200+ entries for a few unique facts)
• Output is unreadable
• Sync results are polluted with noise

Suggested Fix

In merge_memory():

• For raw-file entries: deduplicate on (source_tool, source_file)
• For manual entries: deduplicate on entry_id
• For legacy entries: deduplicate on content hash or entry_id