feat(mem0-plugin): power-user skills + expanded mem0.md config (Tier 8)

Power-user tier:
- /mem0:remember: quick-add with auto-classification, infer=False, confidence=1.0
- /mem0:forget: search-confirm-delete flow with numbered list
- /mem0:pin: mark memories as pinned via metadata update
- /mem0:peek: compact one-liner search results
- parse_mem0_config.py: expanded to parse ## Search, ## Categories, ## Identity
- on_session_start.sh: inject mem0.md project config into session context

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

@@ -0,0 +1,48 @@
+---
+name: mem0-pin
+description: >
+  Pin important memories so they surface prominently. Updates metadata to mark
+  a memory as pinned. Pinned memories should be prioritized during search.
+  TRIGGER: user runs /mem0:pin <query or ID>, or says "pin this memory",
+  "mark as important", "always remember this".
+---
+
+# Mem0 Pin
+
+Pin a memory to mark it as high-priority.
+
+## Execution
+
+### Step 1: Find the memory
+
+The user provides either a search query or memory ID.
+
+**If memory ID:**
+- Call `get_memory` with the ID.
+
+**If search query:**
+- Call `search_memories` with the query, `user_id`, `app_id`, `limit=5`.
+- Show numbered list with content previews.
+- Ask: "Which memory to pin? Enter a number."
+
+### Step 2: Pin it
+
+Call `update_memory` with:
+- `memory_id=<selected_id>`
+- `metadata={"pinned": true}`
+
+The `pinned: true` metadata flag signals importance. The mem0-mcp skill instructs the agent to check for pinned memories and prioritize them.
+
+### Step 3: Confirm
+
+```
+Pinned: "<memory content, first 80 chars>..."
+Memory ID: <id>
+Pinned memories surface first when relevant to a search.
+```
+
+### Unpin
+
+If the user says "unpin" or the memory is already pinned:
+- Call `update_memory` with `metadata={"pinned": false}`
+- Print: `Unpinned: "<content>..."`