feat(spx-gui): support local reference images for generated assets

[CORCTON]

Summary

• Add local reference-image upload for default sprite, costume, animation, and backdrop generation.
• Let costume and animation generation switch between adopted costumes and retained local images; backdrop references remain optional.
• Keep local images when switching presets and remove them only through explicit delete actions.
• Remove local animation-reference backgrounds, then apply the same Kodo FOP used by generated costumes before video generation.
• Persist reference files and task state, and cover upload cancellation and generation restoration.
• Reuse the local-reference upload button and popover across default sprite and backdrop settings.
• Extend AIGCBackdropSettings with optional referenceImageUrl.

Closes #2786

Backend dependency

Backdrop reference-image generation requires https://github.com/goplus/builder-backend/pull/371. Deploy the backend change before enabling this frontend behavior; older backends ignore referenceImageUrl and fall back to text-only backdrop generation.

Validation

• vue-tsc --build --force
• vitest --run src/models/spx/gen src/components/asset/gen/common/param-settings/ParamSelector.test.ts src/components/asset/gen/common/ReferenceImageButton.test.ts (139 tests)
• ESLint on modified frontend files
• Real Qiniu ImageService.Edit smoke test with a local reference image (4:3, one output); compared against the existing text-only path

[CORCTON]

/review -claude

[fennoai]

Review: local image reference support

Solid, well-tested PR. The selection state is centralized in reference-image.ts, validation is applied consistently at the construct/set/save/load boundaries, and generation flows thread a merged AbortSignal through cleanly. The path-traversal guard in loadReferenceImageFile and the raw-Kodo-URL check in toCostumeReferenceImageUrl are nicely defensive and covered by tests. No blocking or correctness issues found — the notes below are maintainability/consistency items.

Non-blocking observations (not inlined):

• The abort/cancel/merge-signal boilerplate in genImages/generate/runGenerateVideo + cancel() is now duplicated across all four *-gen.ts files (backdrop, sprite, costume, animation). Each repeats: abort the prior AbortController with a new Cancelled(...), cancel+dispose+null the prior task, create a fresh controller, mergeSignals(this.getSignal(), ctrl.signal), run the phase, and reset the field only if (this.xCtrl === ctrl). Only the Cancelled message differs. Worth extracting a shared helper so the four copies (and the subtle === ctrl guard) don't drift.
• reference-image.ts allows SVG as a reference upload (imgExts includes svg). No active XSS today since previews flow through useFileUrl → object URL → <img>, but it's a latent stored-XSS surface if any future code renders the file via v-html/inline <svg>. Consider excluding SVG, or keep any rendering in a non-executing image context. Client-side type validation is extension/MIME-based only, so authoritative content validation should live server-side.