fix(video-agent-kit): retain videos without scene cuts

[Ricardo-M-L]

Plugin type (required) / 插件类型（必填）

• UI Plugin / 是 UI 插件 — provides MCP Apps interactive pages / 提供 MCP Apps 交互页面
• Standard plugin / 普通插件（非 UI） — does not provide MCP Apps interactive pages / 不提供 MCP Apps 交互页面
• Not applicable / 不适用 — repository-only changes; no plugin content changed / 仅仓库级改动，不涉及插件内容

Affected plugin name(s) / 涉及的插件名称：video-agent-kit (Standard plugin)

What / 改动内容

detect_shots returns zero shots for a video with no scene cuts because PySceneDetect excludes an uncut scene by default. Both normal and frame-skipping detection are affected, and the empty result can be reused from cache. Downstream recap/editing workflows then lose the entire source video.

Use SceneManager.get_scene_list(start_in_scene=True) in both modes. A two-second uncut video now produces one shot, including when its duration is shorter than min_len. Using the SceneManager API also preserves compatibility with early SceneDetect 0.6 versions whose convenience detect() wrapper lacks the option. Real cut boundaries remain contiguous.

Upgrade the cache contract to cover-all-v3 so old empty caches are rebuilt, synchronize the MCP tool description, add plugin-local real-video regressions and equivalent English/Chinese README notes, and bump both manifests plus the marketplace from 0.4.3 to 0.4.4.

No dependency, permission, network access, or third-party material is added. The tool continues to write the existing shots timeline, rebuilding caches from the older contract.

This is independent of #89 (concat path escaping) and #38 (Python launcher resolution). If another video-agent-kit PR publishes first, this branch will need to rebase and use the next available plugin version.

Validation

• Real FFmpeg-generated uncut/two-scene videos: four regression tests pass with both SceneDetect 0.6.1 and 0.6.7.1. The original code fails five assertions for uncut/short videos and old empty-cache reuse.
• Tests cover normal and frame-skipping detection, a video shorter than min_len, cut continuity, old-cache invalidation, and new-cache reuse. Early SceneDetect end timestamps are allowed their existing one-frame precision difference.
• Root Python suite: 122 tests run, 19 skipped, no failures.
• pnpm install --frozen-lockfile and pnpm build passed with Node.js 24.20.0.
• python3 scripts/validate.py: 34 plugins validated.
• python3 scripts/build_dist.py: 34 artifacts / 292 assets built.
• git diff --check passed.

The tool function was exercised with real FFmpeg and SceneDetect. Installation and invocation inside the ZCode desktop host were not performed.

Self-check / 自查清单

• Plugin name is unique kebab-case; existing fixes retain ownership / 插件名唯一且 kebab-case，已有插件修复保留原归属
• Usage category is set independently of publisher ownership / 用途分类已填写，与维护归属分开
• Plugin type and affected names are declared above / 已声明插件类型与涉及的插件名称
• version bumped in BOTH plugin.json and marketplace.json / 插件清单与市场版本已同步升级
• README.md (EN) and README_CN.md (中文) both updated and equivalent — this legacy official plugin has only a Chinese README.md; the new explanation is provided in both languages in that existing file
• description_i18n has both en and zh-CN / 包含两种语言
• No secrets, machine-specific paths, or private dependencies / 不含密钥、机器专属路径或私有依赖
• Model/API/network dependencies documented / 依赖已写明
• python3 scripts/validate.py and python3 scripts/build_dist.py pass locally / 本地校验与构建均通过

[panda920]

✅ Internal validation passed. A ZCode maintainer will review the change next; after acceptance, release checks run separately and this PR is closed automatically.