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_task_completed.sh

@@ -7,18 +7,21 @@
 # Input:  JSON on stdin with task_id, task_subject, task_description
 # Output: Text that becomes feedback to the model (exit 0)
 
-set -euo pipefail
+# Intentionally omit -e so the reminder always emits even if identity resolution fails.
+set -uo pipefail
 
 if [ -n "${MEM0_DEBUG:-}" ]; then
   mkdir -p "$HOME/.mem0" && exec 2>>"$HOME/.mem0/hooks.log"
 fi
 
 SCRIPT_DIR="$(cd "$(dirname "$0")" && pwd)"
-. "$SCRIPT_DIR/_identity.sh" || true
+. "$SCRIPT_DIR/_identity.sh" 2>/dev/null || true
 
 INPUT=$(cat)
 TASK_SUBJECT=$(echo "$INPUT" | jq -r '.task_subject // "unknown task"' 2>/dev/null || echo "unknown task")
 
+_PROJECT="${MEM0_PROJECT_ID:-unknown}"
+
 cat <<EOF
 Task completed: "$TASK_SUBJECT"
 
@@ -31,7 +34,7 @@ Extract key learnings from this completed task and store them using the mem0 \`a
 
 Memories can be as detailed as needed — include full context, reasoning, code snippets, and examples.
 Only store genuinely useful learnings — skip if the task was trivial.
-Include \`app_id\` = \`"$MEM0_PROJECT_ID"\` as a top-level parameter in every \`add_memory\` call (not in metadata).
+Include \`app_id\` = \`"$_PROJECT"\` as a top-level parameter in every \`add_memory\` call (not in metadata).
 EOF
 
 exit 0