feat: run templates, watch-on-start, and dashboard links

[hbrooks]

What

Three CLI additions on top of the new backend template_id support:

1. Dashboard links — agent run get and agent config get now print a clickable link to the run / agent in the web app. run start prints one too.
2. run start --watch — start a run and immediately stream it (previously --watch only existed on run get). Also adds --interval for the polling fallback, mirroring run get.
3. run start --template <slug> — start from a maintained run template (e.g. welcome-to-ellipsis), sending the backend's new template_id.

agent run start --config <id> --watch      # start + stream
agent run start --template welcome-to-ellipsis
agent run get <run-id>                      # prints a dashboard link
agent config get <config-id>               # prints a dashboard link

URL construction

• Routes (mirrored from the backend's own link format in github_brand.py):
  • run: {app}/{account_login}/agents/runs/{run_id}
  • config: {app}/{account_login}/agents/{config_id}
• account_login isn't on the run/config object, so it's resolved from GET /v1/me (parallelized with the get, so no added latency).
• New resolveAppBase derives the web app base from the API base (api. → app., beta-api. → beta-app.) so beta users get beta-app links, with an ELLIPSIS_APP_BASE override. Replaces the previously-unused APP_BASE constant.

Output hygiene

• config get: the link is written to stderr so the YAML/JSON on stdout stays clean for piping/redirecting; skipped entirely under -o json (machine mode).
• run get/run start/watch: the link is skipped under --json.

Notes

• run start gets a local "exactly one of --config / --config-file / --template" pre-check — clearer than the server's 400 (the server still enforces it).
• Updated the README run-streaming section, which was stale (token-level streaming already ships behind --watch).

Test plan

• bun run typecheck ✓
• bun run test — 62 passing (new urls.test.ts, resolveAppBase cases) ✓
• bun run build + Bun compile smoke + --version ✓
• run start --help / run get --help show the new flags

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