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/scripts/session_stats.py

@@ -42,17 +42,21 @@ def _save(stats: dict) -> None:
         json.dump(stats, f)
 
 
+MAX_RECENT_IDS = 50
+
+
 def init() -> None:
     _save({
         "adds": 0,
         "searches": 0,
         "categories": [],
         "category_counts": {},
+        "recent_ids": [],
         "started": datetime.now().isoformat(),
     })
 
 
-def record_add(category: str = "") -> None:
+def record_add(category: str = "", memory_id: str = "") -> None:
     stats = _load()
     stats["adds"] = stats.get("adds", 0) + 1
     if category:
@@ -60,6 +64,11 @@ def record_add(category: str = "") -> None:
             stats.setdefault("categories", []).append(category)
         counts = stats.setdefault("category_counts", {})
         counts[category] = counts.get(category, 0) + 1
+    if memory_id:
+        recent = stats.setdefault("recent_ids", [])
+        recent.append({"id": memory_id, "category": category, "ts": datetime.now().isoformat()})
+        if len(recent) > MAX_RECENT_IDS:
+            stats["recent_ids"] = recent[-MAX_RECENT_IDS:]
     _save(stats)
 
 
@@ -108,7 +117,8 @@ def main() -> int:
         init()
     elif cmd == "add":
         category = sys.argv[2] if len(sys.argv) > 2 else ""
-        record_add(category)
+        memory_id = sys.argv[3] if len(sys.argv) > 3 else ""
+        record_add(category, memory_id)
     elif cmd == "search":
         record_search()
     elif cmd == "peek":