feat(v2): add /add-vercel skill for agent Vercel deployments

Setup skill that installs Vercel CLI in agent containers and configures
OneCLI credential injection for api.vercel.com. Container skill bundled
in .claude/skills/add-vercel/container-skills/ and copied to
container/skills/ during setup. Also adds dashboard & web apps prompt
to /setup flow (step 5b).

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

.claude/skills/add-vercel/container-skills/vercel-cli/SKILL.md

@@ -0,0 +1,106 @@
+---
+name: vercel-cli
+description: Deploy apps to Vercel. Use when asked to deploy, ship, or publish a web application, or manage Vercel projects, domains, and environment variables.
+---
+
+# Vercel CLI
+
+You can deploy web applications to Vercel using the `vercel` CLI.
+
+## Auth
+
+Auth is handled by OneCLI — the HTTPS_PROXY injects the real token into API requests automatically. The Vercel CLI requires a token to be present to skip its local credential check, so **always pass `--token placeholder`** on every command. OneCLI replaces this with the real token at the proxy level.
+
+Before any Vercel operation, verify auth:
+
+```bash
+vercel whoami --token placeholder
+```
+
+If this fails with an auth error, collect the credential:
+
+```
+trigger_credential_collection(
+  name: "Vercel API Token",
+  hostPattern: "api.vercel.com",
+  headerName: "Authorization",
+  valueFormat: "Bearer {value}",
+  description: "Vercel personal access token. Create one at https://vercel.com/account/tokens"
+)
+```
+
+Then retry `vercel whoami`.
+
+## Deploying
+
+Always use `--yes` to skip interactive prompts and `--token placeholder` for auth (OneCLI replaces with real token).
+
+```bash
+# Deploy to production
+vercel deploy --yes --prod --token placeholder
+
+# Deploy from a specific directory
+vercel deploy --yes --prod --token placeholder --cwd /path/to/project
+
+# Preview deployment (not production)
+vercel deploy --yes --token placeholder
+```
+
+After deploying, verify the live URL:
+
+```bash
+# Check deployment status
+vercel inspect <deployment-url> --token placeholder
+```
+
+If you have `agent-browser` available, open the deployed URL and take a screenshot to visually verify.
+
+## Project Management
+
+```bash
+# Link to an existing Vercel project (non-interactive)
+vercel link --yes --token placeholder
+
+# List recent deployments
+vercel ls --token placeholder
+
+# List all projects
+vercel project ls --token placeholder
+```
+
+## Domains
+
+```bash
+# List domains
+vercel domains ls --token placeholder
+
+# Add a domain to the current project
+vercel domains add example.com --token placeholder
+```
+
+## Environment Variables
+
+```bash
+# Pull env vars from Vercel to local .env
+vercel env pull --token placeholder
+
+# Add an env var (use echo to pipe the value — avoids interactive prompt)
+echo "value" | vercel env add VAR_NAME production --token placeholder
+```
+
+## Common Errors
+
+| Error | Fix |
+|-------|-----|
+| `Error: No framework detected` | Ensure the project has a `package.json` with a `build` script, or set the framework in `vercel.json` |
+| `Error: Rate limited` | Wait and retry. Don't loop — report to user |
+| `Error: You have reached your project limit` | User needs to upgrade Vercel plan or delete unused projects |
+| `ENOTFOUND api.vercel.com` | Network issue. Check proxy connectivity |
+| Auth error after `vercel whoami` | Credential may be expired. Re-run `trigger_credential_collection` |
+
+## Best Practices
+
+- Run `npm run build` locally before deploying to catch build errors early
+- Use `--cwd` instead of `cd` to keep your working directory stable
+- For Next.js projects, `vercel deploy` auto-detects the framework — no extra config needed
+- Use `vercel.json` only when you need custom build settings, rewrites, or headers