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/image/blur-background.md

@@ -2,17 +2,17 @@
 description: Blur the background while keeping the subject sharp using AI.
 ---
 
-# Blur Background
+# Blur Background {#blur-background}
 
 Blur the background of an image while keeping the subject sharp. The AI model isolates the subject, applies a blur to the original background, and composites the sharp subject on top.
 
-## API Endpoint
+## API Endpoint {#api-endpoint}
 
 `POST /api/v1/tools/image/blur-background`
 
 Accepts multipart form data with an image file and a JSON `settings` field.
 
-## Parameters
+## Parameters {#parameters}
 
 | Parameter | Type | Required | Default | Description |
 |-----------|------|----------|---------|-------------|
@@ -20,7 +20,7 @@ Accepts multipart form data with an image file and a JSON `settings` field.
 | feather | integer | No | `0` | Edge feathering radius (0-20) |
 | format | string | No | `"png"` | Output format: `png` or `webp` |
 
-## Example Request
+## Example Request {#example-request}
 
 ```bash
 curl -X POST http://localhost:1349/api/v1/tools/image/blur-background \
@@ -29,7 +29,7 @@ curl -X POST http://localhost:1349/api/v1/tools/image/blur-background \
   -F 'settings={"intensity": 75, "feather": 3}'
 ```
 
-## Example Response
+## Example Response {#example-response}
 
 ```json
 {
@@ -40,7 +40,7 @@ curl -X POST http://localhost:1349/api/v1/tools/image/blur-background \
 
 Track progress via SSE at `GET /api/v1/jobs/{jobId}/progress`. When the job completes, the SSE stream emits a `completed` event with the download URL.
 
-## Notes
+## Notes {#notes}
 
 - This is an AI-powered tool that returns `202 Accepted` and processes asynchronously. Connect to the SSE endpoint to receive progress updates and the final result.
 - Requires the **background-removal** feature bundle to be installed. Returns `501` if the bundle is not available.