feat(inspector): keyframe editing UI + fine-grained backend commands (#95)

[cuic19053-hue]

What

Closes #95 — adds keyframe editing UI + fine-grained backend commands.

Before: the Inspector had a dead diamond toggle button that did nothing. Keyframes were read-only on the timeline (yellow diamonds). Users could not add, delete, move, or change interpolation.

After: clicking the diamond button opens a full keyframe editing panel with per-property rows, draggable diamonds, right-click context menu, and stamp/clear buttons.

How

Backend (Rust) — 4 new EditCommand variants:

Command	Behavior
StampKeyframe	Samples the clip's current value at frame and upserts a keyframe. Uses raw_opacity_at (not opacity_at) to avoid double fade, top_left_at for position, size_at for scale.
RemoveKeyframe	Removes the keyframe at frame. Clears track to None when empty.
MoveKeyframe	Moves a keyframe. Validates: source exists, target within clip range (half-open), target not occupied.
SetKeyframeInterpolation	Changes a keyframe's interpolation_out (Linear/Smooth/Hold).

All commands use absolute timeline frames (public API), converted to clip-relative internally. Each returns affected_clip_ids to trigger frontend refresh.

Tauri boundary: 4 EditRequest variants + into_command mappings, reusing KeyframePropertyDto and domain Interpolation.

Frontend (React + TypeScript):

• KeyframesPanel.tsx — ruler + per-property rows (video: 5 rows, audio: 1 row) + panel-wide playhead overlay
• KeyframesLaneRow.tsx — HTML div diamonds (rotate 45deg, not SVG — avoids percentage coordinate issues), drag with window listeners + snap to playhead (±5 frames), right-click context menu (delete / set interpolation), stamp/clear buttons
• Inspector.tsx — renders <KeyframesPanel> when keyframesOpen === true
• clipRenderer.ts — fix: drawKeyframeMarkers now includes volumeTrack (was missing)

Key design decisions:

• Diamonds use HTML div + transform: rotate(45deg) instead of SVG polygons (SVG points can't take percentage strings; viewBox + preserveAspectRatio="none" distorts diamonds)
• Drag uses useRef cleanup to prevent window listener leaks on unmount
• Drag target clamped to [startFrame, startFrame + duration - 1] (half-open clip range)

Testing

• 12 Rust unit tests (stamp/remove/move/setInterpolation — happy paths + error paths)
• pnpm tsc --noEmit — pass
• pnpm build — pass
• Rust Analyzer IDE diagnostics — 0 errors, 0 warnings
• cargo test / cargo clippy — pending CI (no local Rust toolchain)

Limitations

• SetClipProperties still clears keyframe tracks when setting opacity/volume scalars. The UI to disable scalar sliders for animated properties will be handled in [inspector] 三段式 live 预览缺失 + 字段不全（位置/裁剪/翻转/fade） #97 (Inspector three-section live preview).
• No keyframe curve editor (upstream doesn't have one either).
• No keyboard shortcuts for keyframe operations (Delete to remove, arrow keys to nudge) — future enhancement.

[appergb]

审核通过 ✅(自动审核流程 · 主控亲审 + 路线裁决)

实现 issue #95 关键帧编辑:后端 4 个细粒度 EditCommand(StampKeyframe/RemoveKeyframe/MoveKeyframe/SetKeyframeInterpolation)+ 前端 Inspector KeyframesPanel/KeyframesLaneRow 菱形可拖编辑。

• 命令 apply 语义正确(亲读核对):clip 相对帧 rel=frame-start_frame、半开区间 clip.contains 校验、move 的『目标越界/被占用』守卫、Volume stamp 取 0.0 dB(unity 正确)、SetInterp 仅设 interpolation_out 对齐上游 per-keyframe out-interp。12 后端单测覆盖全部命令与边界。
• 真接线非死代码,Inspector 在 keyframesOpen 渲染 KeyframesPanel(补齐消费缺口),每属性一行 + 拖动/删除/盖章/改插值。
• 符号逐一在 main 存在且匹配,序列化兼容;不碰 #91 媒体重写区;CI 双绿。
• 路线裁决:关键帧采用本 PR 的『后端命令』路线(更接近上游 1:1、走真命令+undo),优于 #120 的纯前端 read-modify-write。先合本 PR 确立该路线。

follow-up(非阻塞):① clipRenderer 把 volumeTrack 加入时间线菱形集,上游仅渲染 5 个视觉轨——与 #120 的音量包络 dot 并存时音频 clip 音量关键帧可能重复渲染,rebase #120 时一并按上游收口;② KeyframesLaneRow 拖拽吸附基于 mousedown 时的 activeFrame 快照(交互细节)。