[feat]: Dreamverse creation studio UI uplift

[aryan5v]

Why

Dreamverse needs a creation-studio lobby that matches the Dreamina-inspired UX direction and speaks the upstream generation_mode wire contract (t2va / fl2va / ref2va) from #1834/#1835. This PR lands the UI layer only so reviewers can judge layout, controls, and protocol fields separately from backend wiring.

Scope

In scope (22 files, ~4.5k LOC in apps/dreamverse/web/):

• CreationComposer, CreationStudio, config pills, preset quick-launch rail, reference upload slots
• generationMode.ts + toGenerationMode() mapping from UI mode ids to upstream wire ids
• Sends generation_mode on session_init_v2 / project_init_v1
• Unit tests: creationConfig.test.ts, generationMode.test.ts
• Playwright smoke: e2e/frontend-shell.spec.ts

Out of scope (follow-up PR on fork):

• Backend creation_config parsing/echo, capability gating, GPU model routing
• Full generation wiring for model/aspect/resolution/duration/image payloads

Tradeoffs

• UI controls for model/resolution/duration are visible before backend honors every field; session init still sends generation_mode plus stubbed/null image fields until backend PR lands.
• In-session config pills are editable in UI but do not push live WS updates yet (matches upstream [feat] Add Dreamverse multimodal inputs and H3 routing #1835 intent to lock mode after start; read-only enforcement is in the backend PR).

Blast Radius

Touches apps/dreamverse/web/ only. No changes to fastvideo/ pipelines, kernels, or Dreamverse Python server. Safe to review as a frontend-only diff; does not affect CI GPU lanes.

Verification

cd apps/dreamverse/web
npm ci
npm run typecheck   # pass
npm test           # 68 passed, 27 skipped
npx playwright test e2e/frontend-shell.spec.ts  # lobby hydration smoke

Manual: open lobby, confirm composer pills, preset rail, and mode picker render; Generate sends WS payload containing generation_mode.

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Fixes #

Checklist

• Added/updated tests for UI helpers and shell smoke
• pre-commit run --all-files (web paths excluded from some hooks; ran npm run typecheck + npm test)
• Documentation update (arch.md backend section deferred to wiring PR)