Add documentation for all PDF tools

docs/tools/page-dimensions.md

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+---
+title: Page Dimensions
+description: Analyze PDF page sizes, orientations, aspect ratios, and rotation. Detect mixed-size documents and export data to CSV.
+---
+
+# Page Dimensions
+
+A diagnostic tool that reads every page in your PDF and reports its exact dimensions, orientation, standard size name, aspect ratio, area, and rotation. Useful for catching mixed-size pages before printing or for documenting the properties of a PDF you received.
+
+## How It Works
+
+1. Upload a PDF file. Analysis starts automatically -- no button to press.
+2. A summary panel shows total pages, number of unique page sizes, and whether the document has mixed sizes.
+3. Browse the full results table with per-page details.
+4. Switch display units between Points, Inches, Millimeters, or Pixels.
+5. Click **Export to CSV** to save the data.
+
+## Reported Fields
+
+| Column        | Description                                 |
+| ------------- | ------------------------------------------- |
+| Page #        | Sequential page number                      |
+| Dimensions    | Width x Height in the selected unit         |
+| Standard Size | Matched name (A4, Letter, etc.) or "Custom" |
+| Orientation   | Portrait or Landscape                       |
+| Aspect Ratio  | Width-to-height ratio as a decimal          |
+| Area          | Page area in the selected unit squared      |
+| Rotation      | Page rotation in degrees                    |
+
+## Features
+
+- Automatic detection of standard paper sizes (A3, A4, A5, Letter, Legal, Tabloid, and more)
+- Mixed-size document warning with a breakdown of which sizes appear and how many pages use each
+- Unit conversion between points, inches, millimeters, and pixels (at 96 PPI)
+- CSV export for use in spreadsheets or documentation systems
+
+## Use Cases
+
+- Verifying all pages are A4 before submitting a document to a print shop
+- Diagnosing why a merged PDF prints with unexpected margins on certain pages
+- Documenting the page layout of a large PDF archive for metadata records
+- Identifying rotated pages that need correction
+
+## Tips
+
+- If the summary shows "Mixed Sizes," use the Fix Page Size tool to standardize before printing.
+- The rotation field helps identify pages that display correctly but have a non-zero rotation attribute, which can cause issues in some workflows.
+
+## Related Tools
+
+- [Fix Page Size](./fix-page-size) -- standardize pages after identifying mixed sizes
+- [Compress PDF](./compress-pdf) -- optimize the PDF after fixing page issues
+- [Rotate PDF](./rotate-pdf) -- correct rotated pages