docs: add authentication guide with 1-year token setup

docs/gateway/authentication.md

@@ -0,0 +1,79 @@
+# Authentication
+
+Clawdbot uses Claude Code's authentication system for API access. By default, OAuth tokens expire every ~24 hours, requiring frequent re-authentication. For a better experience, you can set up a long-lived token that lasts **1 year**.
+
+## Long-Lived Token Setup (Recommended)
+
+Instead of daily re-auth, set up a 1-year token:
+
+```bash
+claude setup-token
+```
+
+This command will:
+1. Prompt you to visit the Anthropic console
+2. Create or copy an API key
+3. Store it for Claude Code (and Clawdbot)
+
+After running `setup-token`, sync the credentials to Clawdbot:
+
+```bash
+clawdbot doctor --yes
+```
+
+## Checking Auth Status
+
+To check your current authentication status:
+
+```bash
+# If you have the auth scripts installed
+~/clawdbot/scripts/claude-auth-status.sh
+
+# Or check manually
+cat ~/.claude/.credentials.json | jq '.claudeAiOauth.expiresAt'
+```
+
+## How It Works
+
+1. **Claude Code** stores credentials in `~/.claude/.credentials.json`
+2. **Clawdbot** syncs from Claude Code to `~/.clawdbot/agents/main/agent/auth-profiles.json`
+3. The `clawdbot doctor --yes` command triggers this sync automatically
+
+## Token Types
+
+| Type | Duration | Setup |
+|------|----------|-------|
+| OAuth (default) | ~24 hours | Automatic on first run |
+| Long-lived token | 1 year | `claude setup-token` |
+
+## Troubleshooting
+
+### "No credentials found" error
+
+Run the doctor to sync credentials:
+
+```bash
+clawdbot doctor --yes
+```
+
+Then restart the service:
+
+```bash
+systemctl --user restart clawdbot
+```
+
+### Token expired
+
+If your token has expired, run `claude setup-token` again in a terminal (not from within Claude Code, as it requires an interactive TTY).
+
+### Checking token expiry
+
+```bash
+# Check both Claude Code and Clawdbot auth
+cat ~/.claude/.credentials.json | jq '.claudeAiOauth.expiresAt' | xargs -I{} date -d @$(({}/1000))
+```
+
+## Requirements
+
+- Claude Max or Pro subscription (for `setup-token`)
+- Claude Code CLI installed (`claude` command available)