feat: creative-agent docs polish + CLI warns on removed flags

[bokelley]

Summary

Bundles two small, thematically related improvements that surfaced from reviewing scope3data/agentic-adapters#100 (AudioStack creative transformer):

Docs (closes #838, #839, #840) — The typed buildCreativeResponse/buildCreativeMultiResponse helpers and audioAsset({...}) factory already shipped. Integrators weren't finding them.

• scripts/generate-agent-docs.ts — TOOL_GOTCHAS data map drives **Watch out:** blocks below the Response section for build_creative, preview_creative, list_creative_formats. Easy to extend per tool.
• docs/llms.txt regenerated.
• skills/build-creative-agent/SKILL.md — cross-cutting pitfalls mention audioAsset, asset-values lists the audio shape, and a new #### Audio creative-template (TTS / mix / master) subsection covers type: 'audio', renders: [{ role, duration_seconds }], async render pipelines, and a handler using buildCreativeResponse + audioAsset.

CLI (closes #842) — --platform-type was removed in 5.1 but the CLI was silently dropping it. Third-party CI scripts that still pass it believe they're filtering agent selection when they aren't.

• bin/adcp.js — storyboard run and its comply alias now emit a stderr warning naming the flag, removal version, and migration path. Suppressed under --json. Detection covers --flag value and --flag=value forms.
• REMOVED_FLAGS is a single data map for future deprecations.
• test/lib/cli-removed-flags.test.js — 5 spawn-based tests.

Out of scope

• feat(sdk): add audioAsset({...}) factory #836 and feat(sdk): typed buildCreativeResponse / buildCreativeMultiResponse helpers #837 — closed on review, the factories and response helpers already shipped (prior releases).
• feat(cli): adcp storyboard run --no-sandbox to force real-adapter responses #841 (--no-sandbox) — deferred pending convention RFC. See thread.

Test plan

• npm run generate-agent-docs — idempotent ("up to date" on second run)
• npm run typecheck — clean
• node --test test/lib/cli-removed-flags.test.js — 5/5 pass
• Manual: adcp storyboard run test-mcp --platform-type creative_transformer --dry-run capability_discovery emits the expected warning
• Manual: same command with --json keeps stdout pure JSON
• Read-through of regenerated docs/llms.txt and SKILL.md — new content reads cleanly

🤖 Generated with Claude Code

[bokelley]

Expert reviews addressed in bdbfded. Ran three experts in parallel: code-reviewer, docs-expert, dx-expert.

Fixed (all three reviewers converged):

• [code-reviewer blocker] CLI tests were hitting the live network because `runFullAssessment` doesn't honor `--dry-run`. Rewrote tests to call with no agent arg → exits at Usage check (2) before any network call. Added 10s `spawnSync` timeouts. Added an advisory-exit test.
• [code-reviewer + dx-expert blocker] `--json` suppressed the stderr warning — wrong call. stderr doesn't pollute stdout JSON, and `--json` mode in CI is precisely where the warning needs to land. Removed the `jsonOutput` guard; flipped the test.
• [code-reviewer] Generator now fails loud if any `TOOL_GOTCHAS` key doesn't resolve to a real tool. A tool rename would otherwise silently drop its "Watch out:" block from llms.txt.
• [code-reviewer + dx-expert] Warning prefix `[warn]` → `DEPRECATED:` for consistency with the existing comply-alias banner (`bin/adcp.js:995`).

Fixed (docs-expert):

• Split the long cross-cutting pitfalls bullet into two (shape-rules + asset-factory-rules).
• Split audio code block into two fenced blocks (format decl, then handler with the `import`) so the import isn't visually nested inside a `listCreativeFormats` literal.
• Added third delta note to the audio subsection: "Inputs are text assets keyed by `asset_id` — read `.content`, not `.text`."
• Added pointer from the async-renders paragraph to the Webhooks section for the task-worker / `creative_review` pattern.
• Fixed pre-existing text-asset shape doc (was `{ text: string }`, schema says `{ content: string }`).

Deferred with notes:

• `--strict-flags` exit mode (dx-expert nice-to-have): sensible next PR, doesn't belong in this one.
• Widen `warnRemovedFlags` to other command dispatchers (`storyboard list/show/step`, top-level `adcp <protocol>`): `--platform-type` was specifically a compliance-run flag; widening risks spurious warnings. Can revisit when a second removed flag lands.
• `audioRender` / `displayRender` render helpers (dx-expert nice-to-have): separate SDK PR — worth opening as a follow-up issue.
• Runtime hint when a `build_creative` response has top-level `tag_url`/`creative_id`/`media_type` and no `creative_manifest` (dx-expert): separate validator PR.

Tests: 6/6 pass, ~3s total. Typecheck clean. Generator idempotent.