[feat]: wire Dreamverse creation studio backend and capabilities

[aryan5v]

Why

Dreamverse creation studio sends model, mode, aspect ratio, resolution, duration, and reference images over the websocket, but the server did not parse, validate, or apply those fields end-to-end. This PR wires session init, echoes resolved creation_config, enforces per-model capabilities, and routes creation overrides into generation.

Scope

Backend (apps/dreamverse/dreamverse/):

• session_creation_config.py — parse/validate model, generation_mode, aspect, resolution, duration
• creation_capabilities.py + GET /creation-capabilities — caps for fast-ltx2, fast-ltx23, fast-h3
• session/controller.py, gpu_pool.py, ltx2_generation.py — per-step overrides; fix LTX2 frame-size crash
• Reference image validation; mock_server.py parity
• Wire field: generation_mode (t2va / ref2va; fl2va rejected)

Frontend wiring (apps/dreamverse/web/):

• creationPayload.ts, creationCapabilities.ts — init payload, capability fetch, client validation
• Read-only in-session config pills until live WS updates exist

Note: This branch includes the creation studio UI uplift commits if they are not on main yet. If the UI PR lands first, GitHub will shrink this diff to backend-only.

Tradeoffs

• H3 uses fixed 768×1344 output; lobby caps constrain UI for fast-h3.
• FL2VA rejected until upstream [Feature] Add Dreamverse mode selection for T2VA, FL2VA, and Ref2VA #1834 backend routing lands.
• GPU model reload on project_init_v1 mid-websocket is a known follow-up.

Blast Radius

apps/dreamverse/ only. No fastvideo/ pipeline or kernel changes.

Verification

cd apps/dreamverse/web && npm run typecheck && npm test
# 80 passed, 27 skipped

PYTHONPATH=apps/dreamverse python3 -m pytest \
  apps/dreamverse/dreamverse/tests/test_creation_capabilities.py \
  apps/dreamverse/dreamverse/tests/test_session_creation_config.py
# 15 passed

Mock-server smoke: uvicorn dreamverse.mock_server:app + Next.js with BACKEND_PORT=8009.

---

Fixes #

Checklist

• Unit tests for capabilities + session creation config
• Frontend typecheck + unit tests pass
• pre-commit run --all-files
• GPU smoke on real Dreamverse deployment

[mergify]

Pre-commit checks failed

Hi @aryan5v, the pre-commit checks have failed. To fix them locally:

# Install pre-commit if you haven't already
uv pip install pre-commit
pre-commit install

# Run all checks and auto-fix what's possible
pre-commit run --all-files

Common fixes:

• yapf: yapf -i <file> (formatting)
• ruff: ruff check --fix <file> (linting)
• codespell: codespell --write-changes <file> (spelling)

After fixing, commit and push the changes. The checks will re-run automatically.

For future commits, pre-commit will run automatically on changed files before each commit.

[mergify]

This PR has merge conflicts with the base branch. Please rebase:

git fetch origin main
git rebase origin/main
# Resolve any conflicts, then:
git push --force-with-lease

[Davids048]

Merged into https://github.com/hao-ai-lab/FastVideo/tree/ds8/dreamversev2-dev through #1856