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-loudnorm.md

@@ -2,21 +2,21 @@
 description: Normalize video audio volume to broadcast standard.
 ---
 
-# Normalize Audio
+# Normalize Audio {#normalize-audio}
 
 Normalize video audio volume to the EBU R128 broadcast loudness standard.
 
-## API Endpoint
+## API Endpoint {#api-endpoint}
 
 `POST /api/v1/tools/video/video-loudnorm`
 
 Accepts multipart form data with a video file. This tool has no configurable settings.
 
-## Parameters
+## Parameters {#parameters}
 
 This tool has no parameters. It applies EBU R128 loudness normalization to the audio track.
 
-## Example Request
+## Example Request {#example-request}
 
 ```bash
 curl -X POST http://localhost:1349/api/v1/tools/video/video-loudnorm \
@@ -24,7 +24,7 @@ curl -X POST http://localhost:1349/api/v1/tools/video/video-loudnorm \
   -F "file=@clip.mp4"
 ```
 
-## Example Response
+## Example Response {#example-response}
 
 ```json
 {
@@ -35,7 +35,7 @@ curl -X POST http://localhost:1349/api/v1/tools/video/video-loudnorm \
 }
 ```
 
-## Notes
+## Notes {#notes}
 
 - Uses FFmpeg's `loudnorm` filter targeting -16 LUFS integrated loudness with -1.5 dBTP true peak and 11 LU loudness range (EBU R128 broadcast standard).
 - The source audio sample rate is preserved in the output.