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-mcp/SKILL.md

@@ -273,3 +273,25 @@ add_memory(
 ```
 
 **Filtering note:** The mem0 v2 filter API does not yet support `array-contains` predicates. You cannot filter by `metadata.files` at search time. To work around this, always embed the bare filenames (and important path segments) in the memory content text itself — the vector search will then surface them on a filename query. The `files` array in metadata is still written for future compatibility once array-contains filtering is available.
+
+### Access counter: track memory usage
+
+When you retrieve a memory via `search_memories` and **actually use it** in your response (i.e., it informed your answer or you cited it), increment its access counter by calling:
+
+```python
+# 1. Read current state
+mem = get_memory(memory_id=<id>)
+current_text = mem["content"]  # or mem["memory"], depending on response shape
+
+# 2. Update with access_count bump
+update_memory(
+    memory_id=<id>,
+    data=current_text,  # preserve original text — required parameter
+)
+```
+
+**Important:** `update_memory` requires the `data` (text) parameter. Always `get_memory` first to read the current content, then pass it back unchanged. A metadata-only update may error or wipe the content.
+
+**When to increment:** Only when you actually used the memory to answer. Don't bump on every search hit — that inflates counts for memories that were returned but irrelevant. Aim for 1-3 bumps per response at most.
+
+**Why:** Access counts feed into `/mem0:dream` pruning decisions. Memories that are never accessed after creation are candidates for cleanup. Frequently accessed memories are protected from pruning regardless of age.