feat: add MemPalace memory provider plugin

plugins/memory/mempalace/README.md

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+# MemPalace — Hermes Memory Provider Plugin
+
+[MemPalace](https://github.com/milla-jovovich/mempalace) integration for
+[Hermes Agent](https://github.com/NousResearch/hermes-agent). Stores verbatim
+conversations in a ChromaDB-backed memory palace with semantic search and a
+temporal knowledge graph.
+
+**96.6% LongMemEval R@5** — the highest recall score ever published for an AI
+memory system. Local-only, zero API calls, free.
+
+## Install
+
+```bash
+pip install mempalace    # pulls in chromadb
+hermes memory setup      # select "mempalace"
+```
+
+Or manually in `~/.hermes/config.yaml`:
+
+```yaml
+memory:
+  provider: mempalace
+```
+
+## How It Works
+
+MemPalace uses a 4-layer memory stack:
+
+| Layer | What | Tokens | When |
+|-------|------|--------|------|
+| L0 | Identity (`~/.mempalace/identity.txt`) | ~100 | Always (system prompt) |
+| L1 | Essential Story (top 15 drawers) | ~500-800 | Always (system prompt) |
+| L2 | On-Demand (wing/room filtered) | ~200-500 | Tool call |
+| L3 | Deep Search (full semantic) | unlimited | Tool call / prefetch |
+
+Conversations are stored verbatim — no summarization, no extraction. The
+philosophy: store everything, make it findable.
+
+## Tools Exposed
+
+| Tool | Description |
+|------|-------------|
+| `palace_search` | Semantic search across all memories |
+| `palace_store` | Store a new memory with wing/room/importance |
+| `palace_browse` | Navigate the palace structure (wings, rooms, counts) |
+| `palace_kg` | Knowledge graph: query, add, timeline, invalidate |
+| `palace_status` | Palace stats and layer info |
+
+## Lifecycle Hooks
+
+- **`sync_turn`** — Every conversation turn is stored as a drawer (background thread)
+- **`on_session_end`** — Full session is archived with high importance
+- **`on_pre_compress`** — Saves context before Hermes discards it during compression
+- **`on_memory_write`** — Mirrors built-in memory writes (add/replace) to the palace
+
+## Configuration
+
+In `~/.hermes/config.yaml`:
+
+```yaml
+plugins:
+  mempalace:
+    palace_path: ~/.mempalace/palace     # ChromaDB storage location
+    wing: hermes                         # default wing for conversations
+    kg_enabled: true                     # temporal knowledge graph
+    identity_path: ~/.mempalace/identity.txt
+```
+
+## Palace Architecture
+
+```
+Palace (ChromaDB)
+├── Wings (projects/topics)
+│   ├── hermes/
+│   │   ├── conversation    — live turn-by-turn storage
+│   │   ├── session_archive — end-of-session consolidated
+│   │   ├── precompress     — saved before context compression
+│   │   ├── memory_user     — mirrored from built-in USER.md
+│   │   ├── memory_memory   — mirrored from built-in MEMORY.md
+│   │   └── general         — explicit palace_store calls
+│   └── (other wings...)
+└── Knowledge Graph (SQLite)
+    ├── Entities (people, projects, tools)
+    └── Triples (subject → predicate → object, with temporal validity)
+```
+
+## Credits
+
+- [MemPalace](https://github.com/milla-jovovich/mempalace) by Ben Sigman ([@bensig](https://github.com/milla-jovovich))
+- [Hermes Agent](https://github.com/NousResearch/hermes-agent) by Nous Research
+- Plugin by Jean Clawd van Amsterdam