[feat] Connect Dreamverse creation settings to generation

[Davids048]

Purpose

Connect Dreamverse creation settings to server validation and generation. The browser sends model, mode,
aspect ratio, resolution, duration, and reference-image inputs; the server resolves and echoes the configuration.

This draft carries the additional changes from #1854 beyond the UI uplift merged in #1853, targeting
ds8/dreamversev2-dev for review and refactoring.

Changes

• Add per-model creation capabilities and the /creation-capabilities endpoint.
• Parse session creation settings and pass dimensions and frame counts through the worker request path.
• Serialize reference-image inputs and validate supported creation selections in the frontend.
• Display the resolved session settings as read-only controls.
• Include the source capability/configuration tests and architecture documentation.

Source verification

The patch is byte-for-byte identical to the difference between these author branches:

• UI uplift: aryan5v/dreamverse-ui-uplift-9f15 at 90d739a91892302edf37c4b23f807f402c83071d.
• Backend wiring: aryan5v/dreamverse-backend-wiring-9f15 at 8c5ee9b51cc3b75f4eba9cb3904fe08578c9dc9e.

Base: e57543b79dd556e5fc5d264f33328f9021072e46 on ds8/dreamversev2-dev.
Diff: 28 files, 1,540 insertions, 86 deletions. Changes outside those paths remain identical to the dev base.

Test Plan

Run from the repository root:

PYTHONPATH=apps/dreamverse:. python -m pytest \
  apps/dreamverse/dreamverse/tests/test_creation_capabilities.py \
  apps/dreamverse/dreamverse/tests/test_session_creation_config.py \
  apps/dreamverse/dreamverse/tests/test_session_init_image.py \
  apps/dreamverse/dreamverse/tests/test_generation_worker.py \
  apps/dreamverse/dreamverse/tests/test_mock_server.py -q
npm --prefix apps/dreamverse/web run typecheck
npm --prefix apps/dreamverse/web test -- --maxWorkers=4
git diff --name-only -z e57543b79dd556e5fc5d264f33328f9021072e46 HEAD | xargs -0 pre-commit run --files

Test Results

• Backend: 25 passed.
• Frontend typecheck: passed.
• Frontend tests: 80 passed, 27 skipped.
• Patch provenance and whitespace checks: passed.
• Pre-commit: inherited yapf formatting failures and a mypy error at
  session_creation_config.py:102 (int(object)). Hook-generated changes were excluded to preserve the source patch.
• GPU generation was not run for this transfer.

Known issues for refactoring

The source implementation retains the issues identified during review:

• LTX dimensions use 32-pixel alignment while refinement requires 64; the default 720p request fails validation.
• Changing models through project_init_v1 updates configuration without reloading the worker.
• A delayed capability response can overwrite lobby selections.
• The advertised 15 MiB image limit can exceed the WebSocket message limit after base64 encoding.
• Invalid model IDs and some invalid durations are silently replaced with defaults.
• H3 configuration metadata disagrees with the backend's fixed geometry and frame count.
• Mock generation enforces the global segment cap instead of the requested project cap.

The inherited UI also needs Enter-key submission and reference-image removal/reset fixes.
FL2AV and 4K remain explicitly unsupported by the source capability contract.

Checklist

• Verified the exact backend-wiring minus UI-uplift patch.
• Ran frontend typechecking and unit tests.
• Ran targeted backend tests.
• Included source tests and documentation.
• Resolve inherited pre-commit failures.
• Resolve generation and UI findings before marking ready for merge.
• Complete GPU validation before merging.