OpenClaw: bring to summary-lifecycle parity with the other five agents

## Background

After the work on branch `embedding_generation`, five of the six supported agents are at full summary-lifecycle parity:

- **Capture**: every user prompt + tool call lands in the `sessions` table with a 768-dim `message_embedding` and `agent=""`.
- **Periodic summary**: a wiki-worker spawns when the per-session summary-state sidecar trips one of three triggers (first-chat at ≥10 msgs, every-N-messages, every-N-hours).
- **Final summary**: a wiki-worker spawns on `session_end` / `Stop` / equivalent.
- **Lock coordination**: a per-session `~/.claude/hooks/summary-state/.lock` (shared across all agents — UUID session ids prevent collision) prevents periodic + final from racing.
- **summary_embedding**: every memory row gets a 768-dim summary vector via the canonical embed-daemon at `~/.hivemind/embed-deps/embed-daemon.js`.

Agents at parity:

- ✅ Claude Code (canonical)
- ✅ Codex
- ✅ Cursor (`cursor-agent --print --model X --force`)
- ✅ Hermes (`hermes -z --provider X -m Y --yolo`)
- ✅ Pi (`pi --print --provider X --model Y`)

## What's missing

**OpenClaw is the only agent not yet at parity.** It was deferred during the multi-agent rollout because its plugin lives in-process (extension-style, similar to Pi but with different lifecycle hooks) rather than as external subprocess hooks. None of the new pieces have been wired into it:

- No periodic-summary trigger logic in the OpenClaw extension.
- No `spawn-wiki-worker` for OpenClaw, no `wiki-worker.js` bundle entry, no install step that drops it into the OpenClaw plugins dir.
- No agent-tagged capture (capture currently doesn't set `agent=\"openclaw\"`).
- No source-level lock-in tests like \`hermes-wiki-worker-source.test.ts\` / \`cursor-wiki-worker-source.test.ts\`.
- No README env-var documentation (\`HIVEMIND_OPENCLAW_PROVIDER\` / \`HIVEMIND_OPENCLAW_MODEL\`) — the knobs don't exist yet.

## Suggested approach

Mirror the Pi rollout, since both agents are in-process extensions:

1. Fork \`src/hooks/codex/wiki-worker.ts\` → \`src/hooks/openclaw/wiki-worker.ts\`. Shell out to the OpenClaw equivalent of \`pi --print\` (whatever the OpenClaw oneshot CLI is — needs a quick check of the OpenClaw README).
2. Fork \`src/hooks/codex/spawn-wiki-worker.ts\` → \`src/hooks/openclaw/spawn-wiki-worker.ts\` with \`findOpenclawBin\`, hooks dir at \`~/.openclaw/hooks\`, env vars \`HIVEMIND_OPENCLAW_PROVIDER\` / \`HIVEMIND_OPENCLAW_MODEL\`.
3. Add the in-process triggers to \`openclaw/extension-source/hivemind.ts\` (or wherever the OpenClaw extension lives) — mirror the Pi pattern: \`bumpTotalCount\` / \`shouldTriggerNow\` / \`tryAcquireLock\` / spawn detached wiki-worker; final summary on \`session_shutdown\`.
4. Tag capture rows \`agent=\"openclaw\"\`.
5. Add a bundle entry in \`esbuild.config.mjs\` for \`openclaw/bundle/wiki-worker.js\`; update the install step to deposit it.
6. Add a source-level lock-in test (\`claude-code/tests/openclaw-wiki-worker-source.test.ts\`) following the same shape as the hermes/cursor ones.
7. README config table: add the two new env-var rows.
8. E2E: tmux-driven session, force \`HIVEMIND_SUMMARY_EVERY_N_MSGS=2\`, verify a memory row + sessions rows with 768-dim embeddings and \`agent=\"openclaw\"\`.

## Acceptance criteria

- A \`hivemind install\` (or \`hivemind openclaw install\`) on a machine with OpenClaw deposits \`wiki-worker.js\` and wires the extension exactly like Pi.
- An OpenClaw session with \`HIVEMIND_SUMMARY_EVERY_N_MSGS=2\` and \`HIVEMIND_DEBUG=1\` produces:
- N+ rows in sessions with \`agent=\"openclaw\"\` and \`message_embedding\` length 768
- ≥1 row in memory with \`agent=\"openclaw\"\` and \`summary_embedding\` length 768 after either the periodic threshold trips or the final session ends
- Source-level test passing: locks the spawn shape, agent label, env-var defaults, hooks dir, and the \`spawnOpenclawWikiWorker\` export.

## Out of scope

- Switching OpenClaw from extension-style to external subprocess hooks. Keep the in-process model — Pi proved this works fine.

## Context links

- \`claude-code/tests/cursor-wiki-worker-source.test.ts\` and \`claude-code/tests/hermes-wiki-worker-source.test.ts\` — source-level test pattern to mirror.
- \`src/hooks/pi/wiki-worker.ts\` and \`pi/extension-source/hivemind.ts\` — closest architectural reference (in-process extension).
- Branch where the other five agents reached parity: \`embedding_generation\`.