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/data/csv-json.md

@@ -0,0 +1,57 @@
+---
+description: Convert between CSV and JSON, both directions.
+---
+
+# CSV to JSON
+
+Convert between CSV and JSON formats in both directions. Upload a CSV or TSV file to get a JSON array of objects, or upload a JSON array to get a CSV file.
+
+## API Endpoint
+
+`POST /api/v1/tools/data/csv-json`
+
+Accepts multipart form data with a CSV, TSV, or JSON file and a JSON `settings` field.
+
+## Parameters
+
+| Parameter | Type | Required | Default | Description |
+|-----------|------|----------|---------|-------------|
+| pretty | boolean | No | `true` | Pretty-print JSON output with indentation |
+
+## Example Request
+
+CSV to JSON:
+
+```bash
+curl -X POST http://localhost:1349/api/v1/tools/data/csv-json \
+  -H "Authorization: Bearer si_your-api-key" \
+  -F "file=@users.csv" \
+  -F 'settings={"pretty": true}'
+```
+
+JSON to CSV:
+
+```bash
+curl -X POST http://localhost:1349/api/v1/tools/data/csv-json \
+  -H "Authorization: Bearer si_your-api-key" \
+  -F "file=@users.json" \
+  -F 'settings={}'
+```
+
+## Example Response
+
+```json
+{
+  "jobId": "a1b2c3d4-e5f6-7890-abcd-ef1234567890",
+  "downloadUrl": "/api/v1/download/a1b2c3d4-e5f6-7890-abcd-ef1234567890/users.json",
+  "originalSize": 1500,
+  "processedSize": 2200
+}
+```
+
+## Notes
+
+- Conversion direction is auto-detected from the input file extension: `.csv` or `.tsv` produces `.json`, and `.json` produces `.csv`.
+- The `pretty` parameter only affects JSON output. When set to `false`, the output is a compact single-line JSON string.
+- JSON input must be an array of objects with consistent keys. Each object becomes a row, and each key becomes a column header.
+- TSV (tab-separated values) files are supported alongside CSV.