feat(i18n): 21-language pipeline, landing/docs/API wiring, landing+API translations

Shared Claude Code translation pipeline (scripts/i18n, no API key) plus Astro/VitePress/Scalar i18n wiring. Landing and API reference translated into all 20 languages; docs i18n wiring + English source anchors. The translated docs markdown (apps/docs/<locale>/**, 3,620 files) follows in a companion PR because it exceeds GitHub's per-PR CI file limit.

apps/docs/tools/video/video-to-frames.md

@@ -2,17 +2,17 @@
 description: Extract frames from a video as a ZIP of images.
 ---
 
-# Video to Frames
+# Video to Frames {#video-to-frames}
 
 Extract individual frames from a video and download them as a ZIP archive of PNG or JPG images.
 
-## API Endpoint
+## API Endpoint {#api-endpoint}
 
 `POST /api/v1/tools/video/video-to-frames`
 
 Accepts multipart form data with a video file and a JSON `settings` field.
 
-## Parameters
+## Parameters {#parameters}
 
 | Parameter | Type | Required | Default | Description |
 |-----------|------|----------|---------|-------------|
@@ -21,7 +21,7 @@ Accepts multipart form data with a video file and a JSON `settings` field.
 | timestamps | string | No | `""` | Comma-separated timestamps in seconds. Required when mode is `"timestamps"` |
 | format | string | No | `"png"` | Image format for extracted frames: `png`, `jpg` |
 
-## Example Request
+## Example Request {#example-request}
 
 Extract every 30th frame as JPG:
 
@@ -41,7 +41,7 @@ curl -X POST http://localhost:1349/api/v1/tools/video/video-to-frames \
   -F 'settings={"mode": "timestamps", "timestamps": "1.5,5,12.3"}'
 ```
 
-## Example Response
+## Example Response {#example-response}
 
 ```json
 {
@@ -52,7 +52,7 @@ curl -X POST http://localhost:1349/api/v1/tools/video/video-to-frames \
 }
 ```
 
-## Notes
+## Notes {#notes}
 
 - The `all` mode extracts every frame and can produce very large ZIP files for long videos. Use `nth` or `timestamps` mode for selective extraction.
 - PNG preserves full quality but produces larger files. JPG is smaller but lossy.