fix: slim credential docs in group CLAUDE.md and add onecli-gateway container skill

container/skills/onecli-gateway/SKILL.md

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+---
+name: onecli-gateway
+description: >-
+  Handle credentials and authentication for external services. Use when you
+  hit a 401, 403, or app_not_connected error, or when the user asks you to
+  access an external service (Gmail, GitHub, Slack, Calendar, Stripe, etc.).
+  Do NOT use browser extensions or manual auth flows — make HTTP requests
+  directly; the OneCLI proxy injects credentials automatically.
+---
+
+# OneCLI Gateway: Credentials & Authentication
+
+Your container routes all HTTPS traffic through the OneCLI proxy, which
+injects stored credentials (API keys, OAuth tokens) at the proxy boundary.
+You never see or handle credential values directly.
+
+## Making Requests
+
+Call the real API URL. The proxy intercepts and injects credentials automatically.
+
+```bash
+curl -s "https://gmail.googleapis.com/gmail/v1/users/me/messages?maxResults=5"
+curl -s "https://api.github.com/user/repos?per_page=10"
+curl -s "https://api.stripe.com/v1/charges?limit=5"
+```
+
+Any HTTP client (curl, fetch, axios, Python requests, Go net/http, git) honors
+`HTTPS_PROXY` automatically. You do not need to set auth headers.
+
+If a tool or library validates credentials locally before making the request,
+pass any placeholder value (a fake string). The proxy replaces it with real
+credentials at request time.
+
+## When a Request Fails (401 / 403 / app_not_connected)
+
+### Step 1 — Show the user a connect link
+
+If the error response includes a `connect_url`, share it directly:
+
+> To connect [service], open this link:
+> [connect_url from the error response]
+
+If there's no `connect_url`, tell the user to open the OneCLI dashboard and
+connect the service there.
+
+Do NOT ask the user for API keys or tokens. Do NOT suggest pasting credentials
+into chat. The fix is always connecting the service in OneCLI.
+
+### Step 2 — Retry after the user connects
+
+After showing the link, let the user know you'll retry once they've connected.
+When they confirm (or after a reasonable pause), retry the original request.
+
+If the retry still fails, ask the user if they need help with the OneCLI setup.
+
+## Rules
+
+- **Never** say "I don't have access to X" without first making the HTTP
+  request through the proxy.
+- **Never** use browser extensions, gcloud, or manual auth flows. The proxy
+  handles credentials for you.
+- **Never** ask the user for API keys, tokens, or passwords directly.
+- **Never** suggest the user open Gmail/Calendar/GitHub in their browser
+  when they ask you to read or interact with those services. You have API
+  access — use it.
+- If the proxy returns a policy error (403 with a JSON body), respect the
+  block. Do not retry or circumvent it.

container/skills/onecli-gateway/instructions.md

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+# Credentials & External Services
+
+Your HTTP requests go through the OneCLI proxy, which injects real credentials automatically. Just call any API directly (Gmail, GitHub, Slack, etc.) — the proxy adds auth before it reaches the service.
+
+Use any method: curl, Python, a CLI tool, whatever fits. If a tool checks for credentials locally, pass any placeholder value — the proxy replaces it with real credentials at request time.
+
+If you get a `401`/`403`/`app_not_connected`, run `/onecli-gateway` for the full error-handling flow. Never ask the user for API keys or tokens — if credentials are missing, the fix is connecting the service in OneCLI.