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/content-aware-resize.md

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+# Content-Aware Resize
+
+Seam carving resize that intelligently removes or adds pixels along paths of least visual importance, preserving important content and optionally protecting faces.
+
+## API Endpoint
+
+`POST /api/v1/tools/image/content-aware-resize`
+
+**Processing:** Synchronous (returns result directly)
+
+**Model bundle:** None required for basic operation. Face protection uses the `face-detection` bundle (200-300 MB) if enabled.
+
+## Parameters
+
+| Parameter | Type | Required | Default | Description |
+|-----------|------|----------|---------|-------------|
+| file | file | Yes | - | Image file (multipart) |
+| width | integer | No | - | Target width in pixels |
+| height | integer | No | - | Target height in pixels |
+| protectFaces | boolean | No | `false` | Detect and protect faces from seam removal |
+| blurRadius | number | No | `4` | Pre-processing blur radius for energy calculation (0-20) |
+| sobelThreshold | number | No | `2` | Sobel edge detection threshold (1-20). Higher values make the algorithm more aggressive |
+| square | boolean | No | `false` | Resize to a square (uses the smaller dimension) |
+
+At least one of `width`, `height`, or `square` must be specified.
+
+## Example Request
+
+```bash
+curl -X POST http://localhost:13490/api/v1/tools/image/content-aware-resize \
+  -F "file=@landscape.jpg" \
+  -F 'settings={"width":800,"protectFaces":true}'
+```
+
+## Response (200 OK)
+
+```json
+{
+  "jobId": "a1b2c3d4-e5f6-7890-abcd-ef1234567890",
+  "downloadUrl": "/api/v1/download/{jobId}/landscape_seam.png",
+  "originalSize": 450000,
+  "processedSize": 380000,
+  "width": 800,
+  "height": 600
+}
+```
+
+## Notes
+
+- This tool returns a synchronous response (not 202 async). Processing happens inline.
+- Uses the `caire` seam carving library for content-aware resizing.
+- Only reduces dimensions (removes seams). Cannot expand an image beyond its original size.
+- The `protectFaces` option uses AI face detection to mark face regions as high-energy, preventing seams from passing through faces.
+- `blurRadius` controls smoothing before energy map calculation. Higher values make the energy map more uniform, which can help with noisy images.
+- `sobelThreshold` affects how aggressively edges are detected. Lower values preserve more subtle edges.
+- Output is always PNG format.
+- Supports HEIC/HEIF, RAW, TGA, PSD, EXR, and HDR input formats via automatic decoding.