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/on_pre_commit.py

@@ -36,6 +36,25 @@ except ImportError:
 
 
 def get_commit_message() -> str:
+    """Read the current commit message from COMMIT_EDITMSG (pre-commit context).
+
+    Falls back to HEAD's message if COMMIT_EDITMSG doesn't exist yet
+    (e.g., when invoked outside the git hook context).
+    """
+    try:
+        git_dir = subprocess.run(
+            ["git", "rev-parse", "--git-dir"],
+            capture_output=True, text=True, timeout=5,
+        )
+        if git_dir.returncode == 0:
+            editmsg = os.path.join(git_dir.stdout.strip(), "COMMIT_EDITMSG")
+            if os.path.isfile(editmsg):
+                with open(editmsg) as f:
+                    first_line = f.readline().strip()
+                    if first_line and not first_line.startswith("#"):
+                        return first_line
+    except Exception:
+        pass
     try:
         result = subprocess.run(
             ["git", "log", "-1", "--format=%s", "HEAD"],