fix(mem0-plugin): fix 3 critical + 5 important issues from review

Critical fixes:
- C1: Pin/dream update_memory now reads content first via get_memory
  before updating, preventing metadata-only calls that wipe content
- C2: SessionStart memory count uses GET /v3/memories/?page_size=1 for
  real count from pagination envelope instead of search limit=100
- C3: on_task_completed.sh uses ${MEM0_PROJECT_ID:-unknown} to avoid
  crash when identity resolution fails under set -u

Important fixes:
- I1: session_stats.py tracks recent_ids (memory IDs + timestamps) for
  /mem0:forget undo support. Capped at 50 entries.
- I2: /mem0:health --deep mode adds memory quality analysis: duplicate
  detection, stale entry scan, contradiction flags, orphan tagging
- I3: /mem0:stats ASCII histogram for category distribution with bar
  chart, sorted by count descending
- I4: mem0-mcp skill documents access counter pattern: get_memory then
  update_memory to track which memories are actually used
- I5: on_pre_commit.py reads COMMIT_EDITMSG first (current commit),
  falls back to HEAD only if EDITMSG unavailable

Tests: 91 -> 94 (3 new for recent_ids tracking)

mem0-plugin/skills/mem0-health/SKILL.md

@@ -76,3 +76,58 @@ All checks passed. mem0 is healthy.
 ```
 
 If any check fails, add a `## Troubleshooting` section with specific fix steps for each failure.
+
+## Extended mode: Memory Quality Analysis
+
+When invoked with `--deep` (e.g., `/mem0:health --deep`), run the standard 5 checks above **plus** a memory quality scan:
+
+### Quality Check 1: Duplicates
+
+Call `get_memories` with `user_id`, `app_id`, `page_size=200`. Compare all pairs within the same `metadata.type` group for high textual overlap (shared nouns/keywords > 60%). Report:
+
+```
+Potential duplicates: <N> pairs
+  [mem0:<id1>] ≈ [mem0:<id2>] — both about "<shared topic>"
+```
+
+### Quality Check 2: Stale memories
+
+Flag memories where:
+- `metadata.type` is `session_state` or `compact_summary` AND older than 90 days
+- `metadata.confidence` < 0.3 AND older than 30 days
+
+```
+Stale candidates: <N>
+  [mem0:<id>] — session_state, 142d old
+```
+
+### Quality Check 3: Contradictions
+
+Within each `metadata.type` group, flag pairs that assert opposing facts about the same topic. Use semantic judgment — look for negation patterns, conflicting tool/framework choices, or reversed decisions.
+
+```
+Possible contradictions: <N>
+  [mem0:<idA>] vs [mem0:<idB>] — conflicting on "<topic>"
+```
+
+### Quality Check 4: Orphan memories
+
+Memories with no `metadata.type` set, or with `metadata.type` not in the 17 known coding categories. These were likely written without proper tagging.
+
+```
+Untagged/orphan memories: <N>
+```
+
+### Quality summary
+
+```
+## Memory Quality
+| Metric         | Count | Action                          |
+|----------------|-------|---------------------------------|
+| Duplicates     | <N>   | Run /mem0:dream to merge        |
+| Stale          | <N>   | Run /mem0:dream to prune        |
+| Contradictions | <N>   | Run /mem0:dream to resolve      |
+| Orphans        | <N>   | Consider retagging via MCP      |
+```
+
+If all counts are 0: `Memory quality: clean. No duplicates, stale entries, or contradictions found.`