docs: organize tool pages by modality under /tools/<modality>/

Move all 157 tool pages into image/video/audio/pdf/data subfolders so URLs read /tools/<modality>/<id> (e.g. /tools/image/crop). Nest the image sub-categories under an Image group in the sidebar so the nav reads by modality. Add public/_redirects (301, clean + .html forms) mapping every old flat /tools/<id> URL to its new path so inbound links keep working. Rewrite all internal /tools links. Verified with a clean docs build (no dead links).

apps/docs/tools/image/lqip-placeholder.md

@@ -0,0 +1,59 @@
+---
+description: Generate a tiny low-quality image placeholder with base64 data URI.
+---
+
+# LQIP Placeholder
+
+Generate a tiny low-quality image placeholder (LQIP) from a source image. Returns a small placeholder file along with a base64 data URI, ready-to-use HTML `<img>` tag, and CSS `background-image` snippet for immediate embedding.
+
+## API Endpoint
+
+`POST /api/v1/tools/image/lqip-placeholder`
+
+Accepts multipart form data with an image file and a JSON `settings` field.
+
+## Parameters
+
+| Parameter | Type | Required | Default | Description |
+|-----------|------|----------|---------|-------------|
+| width | integer | No | `16` | Target width in pixels (4-64) |
+| blur | number | No | `2` | Blur radius for the blur strategy (0-20) |
+| strategy | string | No | `"blur"` | Placeholder strategy: `blur`, `pixelate`, or `solid` |
+| format | string | No | `"webp"` | Output format: `webp`, `png`, or `jpeg` |
+| quality | integer | No | `50` | Output quality (1-100) |
+
+## Example Request
+
+```bash
+curl -X POST http://localhost:1349/api/v1/tools/image/lqip-placeholder \
+  -H "Authorization: Bearer si_your-api-key" \
+  -F "file=@photo.jpg" \
+  -F 'settings={"width": 20, "strategy": "blur", "format": "webp"}'
+```
+
+## Example Response
+
+```json
+{
+  "jobId": "a1b2c3d4-e5f6-7890-abcd-ef1234567890",
+  "downloadUrl": "/api/v1/download/a1b2c3d4-e5f6-7890-abcd-ef1234567890/photo.webp",
+  "originalSize": 2450000,
+  "processedSize": 280,
+  "dataUri": "data:image/webp;base64,UklGR...",
+  "width": 20,
+  "height": 13,
+  "bytes": 280,
+  "strategy": "blur",
+  "html": "<img src=\"data:image/webp;base64,UklGR...\" width=\"20\" height=\"13\" alt=\"\" />",
+  "css": "background-image: url(data:image/webp;base64,UklGR...);"
+}
+```
+
+## Notes
+
+- The `dataUri` field contains the complete data URI, ready for use in `src` attributes or CSS without any additional requests.
+- The `html` and `css` fields provide copy-paste snippets for common use cases.
+- The `blur` strategy produces a soft, blurred thumbnail. The `pixelate` strategy creates a blocky mosaic. The `solid` strategy returns a single averaged color.
+- Typical placeholder sizes are 200-500 bytes, making them suitable for inlining directly in HTML.
+- Height is calculated automatically to preserve the source image's aspect ratio.
+- HEIC, RAW, PSD, and SVG inputs are automatically decoded before processing.