feat(help): mention agent / CI conventions in root --help

[crowlbot]

Summary

Make deno deploy --help itself surface the agent/CI conventions that landed in #91-#95. Today the global --json, --non-interactive, --token and the DENO_DEPLOY_TOKEN env var are all individually documented in --help line items, but the root command description gives no hint that they exist as a coherent agent-mode contract or that there's a stable exit-code taxonomy.

Tiny change:

• deploy/mod.ts — expand deployCommand.description() to mention DENO_DEPLOY_TOKEN, the recommended --json --non-interactive invocation, the exit-code taxonomy (0–6), and the structured error envelope. Link to docs.deno.com/runtime/reference/cli/deploy/#agent--ci-usage for the full reference.
• deploy/mod.ts — add three .example() entries for the most common agent flows: whoami --json, non-interactive publish, non-interactive create.
• sandbox/mod.ts — expand sandboxCommand.description() to document the DENO_DEPLOY_TOKEN escape hatch and link to the sandbox reference. (Intentionally does not advertise --json / --non-interactive for sandbox, because the standalone deno sandbox command doesn't currently expose those as globals — a separate gap for a follow-up.)

Why root-description and not per-subcommand

--help listings are dense; per-flag descriptions don't compose into a story about "how do I drive this from a bot." A 6-line prose paragraph at the top of the root command's description is the natural place to set that context, alongside a few .example() entries that the agent can pattern-match.

Test plan

deno fmt, deno lint, deno check main.ts, deno test -A — CI runs all four. No behavior change; only --help text.

Companion

The canonical reference URL this links to is being added in denoland/docs#3180.

[crowlbot]

The remaining deno CI failure is the known sandbox-backend flake, not anything in this diff (the changes are text-only — root-command description strings and three .example() entries).

The sandbox copy and sandbox copy directory structure tests have failed on every re-run today with backend errors (SANDBOX_WEBSOCKET_HANDSHAKE_ERROR / DEPLOYMENT_NOT_FOUND / INTERNAL_SERVER_ERROR), same pattern as the other open PRs (#98, #99) and as recent main runs occasionally do. jsr, fmt, lint, check and the other 31 tests all pass.

Happy to re-run once more if you'd like to wait for green, otherwise this should be safe to admin-merge.