Enhance pipeline DAG visibility, add scene-count stat, and minor lint/cleanup

[Flintcore]

Motivation

• Improve maintainability by removing unused variables and reducing lint noise so real issues surface more clearly.
• Enhance observability and UX of the workflow DAG so users can quickly tell which phase is running and see pipeline progress.
• Extend project statistics to include scene/clip counts to provide more complete operational metrics.

Description

• Add a new engineering optimization plan document at docs/engineering-optimization-plan.md outlining quality, observability, and product UX recommendations.
• Clean up error handling in PromptConfigForm by removing an unused exception variable in the catch block to reduce lint warnings.
• Update ProjectStats to rename the Image import to ImageIcon, add a new Clapperboard card for "场次数" (scene/clip count), and adjust the responsive grid to accommodate the extra card.
• Improve PipelineDagView by dropping the unused setEdges variable, auto-selecting the backend-provided currentPhase, computing phase-level metrics (completed/running/failed/total/progress), and rendering a progress bar and current-phase badge in the DAG header.

Testing

• Ran npm run lint across the changed files and resolved the reported warnings so lint completed successfully.
• Performed a TypeScript/build verification with npm run build, which completed without errors.
• Executed the existing automated test suite with npm test, and the suite passed without failures.

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Codex Task

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Note

Low Risk
Low risk UI/UX changes plus small lint cleanups; main risk is minor display/selection logic regressions in the DAG view (e.g., incorrect phase auto-selection or progress counts).

Overview
Improves workflow observability in the workspace by enhancing the pipeline DAG header: it now auto-selects the backend currentPhase, shows an explicit “当前阶段” badge, and renders a progress bar with completed/total plus running/failed counts.

Extends the project stats panel with a new “场次数” card (using clipCount) and updates the icon import (Image -> ImageIcon) and responsive grid to fit the additional metric.

Also includes small maintainability cleanups (remove unused setEdges, simplify catch in PromptConfigForm) and adds docs/engineering-optimization-plan.md outlining follow-up engineering/product optimization recommendations.

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