feat(cli): add version check system with agent-friendly output

- New `updateCheck.ts` utility: cached npm registry check (24h TTL),
  sync `getUpdateMeta()` for _meta envelope, `printUpdateNotice()` for
  passive stderr banner
- `upgrade --check --json`: machine-readable version check for AI agents
  Returns { current, latest, updateAvailable }
- `_meta` envelope on all --json commands (info, lint, benchmark,
  compositions): includes version, latestVersion, updateAvailable
- `doctor` shows version check as first row
- Passive update notice on stderr after command completes (skipped in
  CI, non-TTY, --json, --quiet)
- Background check fires on startup (non-blocking, populates cache)

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

packages/cli/src/commands/info.ts

@@ -6,6 +6,7 @@ import { c } from "../ui/colors.js";
 import { formatBytes, label } from "../ui/format.js";
 import { ensureDOMParser } from "../utils/dom.js";
 import { resolveProject } from "../utils/project.js";
+import { withMeta } from "../utils/updateCheck.js";
 
 function totalSize(dir: string): number {
   let total = 0;
@@ -52,7 +53,7 @@ export default defineCommand({
     if (args.json) {
       console.log(
         JSON.stringify(
-          {
+          withMeta({
             name: project.name,
             resolution: parsed.resolution,
             width: parsed.resolution === "portrait" ? 1080 : 1920,
@@ -62,7 +63,7 @@ export default defineCommand({
             tracks: tracks.size,
             types: typeCounts,
             size,
-          },
+          }),
           null,
           2,
         ),