/add-slack (#366)

* feat: add Slack channel skill (/add-slack)

Slack Bot integration via @slack/bolt with Socket Mode. Can replace
WhatsApp entirely (SLACK_ONLY=true) or run alongside it.

- SlackChannel implementing Channel interface (46 unit tests)
- Socket Mode connection (no public URL needed)
- @mention translation (Slack <@UBOTID> → TRIGGER_PATTERN)
- Message splitting at 4000-char Slack API limit
- Thread flattening (threaded replies delivered as channel messages)
- User name resolution with caching
- Outgoing message queue with flush-on-reconnect
- Channel metadata sync with pagination
- Proper Bolt types (GenericMessageEvent | BotMessageEvent)
- Multi-channel orchestrator changes (conditional channel creation)
- Setup guide (SLACK_SETUP.md) and known limitations documented

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

* local settings

* adjusted when installing

---------

Co-authored-by: Claude Opus 4.6 <noreply@anthropic.com>

.claude/skills/add-slack/modify/src/config.ts.intent.md

@@ -0,0 +1,21 @@
+# Intent: src/config.ts modifications
+
+## What changed
+Added SLACK_ONLY configuration export for Slack channel support.
+
+## Key sections
+- **readEnvFile call**: Must include `SLACK_ONLY` in the keys array. NanoClaw does NOT load `.env` into `process.env` — all `.env` values must be explicitly requested via `readEnvFile()`.
+- **SLACK_ONLY**: Boolean flag from `process.env` or `envConfig`, when `true` disables WhatsApp channel creation
+- **Note**: SLACK_BOT_TOKEN and SLACK_APP_TOKEN are NOT read here. They are read directly by SlackChannel via `readEnvFile()` in `slack.ts` to keep secrets off the config module entirely (same pattern as ANTHROPIC_API_KEY in container-runner.ts).
+
+## Invariants
+- All existing config exports remain unchanged
+- New Slack key is added to the `readEnvFile` call alongside existing keys
+- New export is appended at the end of the file
+- No existing behavior is modified — Slack config is additive only
+- Both `process.env` and `envConfig` are checked (same pattern as `ASSISTANT_NAME`)
+
+## Must-keep
+- All existing exports (`ASSISTANT_NAME`, `POLL_INTERVAL`, `TRIGGER_PATTERN`, etc.)
+- The `readEnvFile` pattern — ALL config read from `.env` must go through this function
+- The `escapeRegex` helper and `TRIGGER_PATTERN` construction