Add /add-deltachat skill

Skill files only — copied from PR #2192 (channels branch).
Source adapter (src/channels/deltachat.ts) lives on the channels
branch and is installed by the skill.

Co-Authored-By: Axel McLaren <scm@axml.uk>
Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

.claude/skills/add-deltachat/REMOVE.md

@@ -0,0 +1,62 @@
+# Remove DeltaChat
+
+## 1. Disable the adapter
+
+Comment out the import in `src/channels/index.ts`:
+
+```typescript
+// import './deltachat.js';
+```
+
+## 2. Remove credentials
+
+Remove the `DC_*` lines from `.env`:
+
+```bash
+DC_EMAIL
+DC_PASSWORD
+DC_IMAP_HOST
+DC_IMAP_PORT
+DC_SMTP_HOST
+DC_SMTP_PORT
+```
+
+## 3. Rebuild and restart
+
+```bash
+pnpm run build
+
+# Linux
+systemctl --user restart nanoclaw
+
+# macOS
+launchctl kickstart -k gui/$(id -u)/com.nanoclaw
+```
+
+## 4. Remove account data (optional)
+
+To fully remove all account data including DeltaChat encryption keys:
+
+```bash
+rm -rf dc-account/
+```
+
+> **Warning:** This deletes the Autocrypt keys. Contacts who have verified your bot's key will need to re-verify if the same email address is re-used with a new account.
+
+To keep the account for later reinstall, leave `dc-account/` intact.
+
+## 5. Remove the package (optional)
+
+```bash
+pnpm remove @deltachat/stdio-rpc-server
+```
+
+## Verification
+
+After removal, confirm the adapter is no longer starting:
+
+```bash
+grep "deltachat" logs/nanoclaw.log | tail -5
+```
+
+Expected: no `Channel adapter started` entry after the last restart.