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/audio/waveform-image.md

@@ -0,0 +1,47 @@
+---
+description: Generate a waveform visualization as a PNG image from an audio file.
+---
+
+# Waveform Image
+
+Generate a waveform visualization as a PNG image from an audio file, with configurable dimensions and color.
+
+## API Endpoint
+
+`POST /api/v1/tools/audio/waveform-image`
+
+Accepts multipart form data with an audio file and a JSON `settings` field.
+
+## Parameters
+
+| Parameter | Type | Required | Default | Description |
+|-----------|------|----------|---------|-------------|
+| width | integer | No | `1024` | Image width in pixels (256 to 3840) |
+| height | integer | No | `256` | Image height in pixels (64 to 1080) |
+| color | string | No | `"#4f46e5"` | Waveform hex color (e.g. `"#4f46e5"`) |
+
+## Example Request
+
+```bash
+curl -X POST http://localhost:1349/api/v1/tools/audio/waveform-image \
+  -H "Authorization: Bearer si_your-api-key" \
+  -F "file=@audio.mp3" \
+  -F 'settings={"width": 1920, "height": 400, "color": "#e07832"}'
+```
+
+## Example Response
+
+```json
+{
+  "jobId": "a1b2c3d4-e5f6-7890-abcd-ef1234567890",
+  "downloadUrl": "/api/v1/download/a1b2c3d4-e5f6-7890-abcd-ef1234567890/audio.png",
+  "originalSize": 4500000,
+  "processedSize": 45000
+}
+```
+
+## Notes
+
+- The output is always a PNG image, regardless of the input audio format.
+- The waveform is rendered on a transparent background.
+- Useful for thumbnails, social media previews, or embedding in web pages.