feat: comprehensive Wino Mail updates

- ReaderView: complete rewrite with CSS styling, headers, attachments, zoom, find, dark mode, image blocking
- Categories: DAO + UI tree widget with colors, nested categories, assignment
- Rules engine: DAO + evaluation + actions (move, mark read, flag, delete, category, forward)
- Templates: DAO + editor + manager with variables support
- Signatures: DAO + manager + auto-per-account + manual selector in compose
- ComposeView: signature combo, template selector, auto-signature on new email
- MainWindow: frameless with rounded corners, 1px border, resize from edges, no status bar
- Database: new tables (Category, MailCategory, Rule, Template, Signature) with indexes

resources/icons/SVG/Broken/Video, Audio, Sound/Gallery Add.svg

@@ -0,0 +1,5 @@
+<svg width="24" height="24" viewBox="0 0 24 24" fill="none" xmlns="http://www.w3.org/2000/svg">
+<path d="M2 12.5001L3.75159 10.9675C4.66286 10.1702 6.03628 10.2159 6.89249 11.0721L11.1822 15.3618C11.8694 16.0491 12.9512 16.1428 13.7464 15.5839L14.0446 15.3744C15.1888 14.5702 16.7369 14.6634 17.7765 15.599L21 18.5001" stroke="black" stroke-width="1.5" stroke-linecap="round"/>
+<path d="M15 5.5H18.5M18.5 5.5H22M18.5 5.5V9M18.5 5.5V2" stroke="black" stroke-width="1.5" stroke-linecap="round"/>
+<path d="M22 12C22 16.714 22 19.0711 20.5355 20.5355C19.0711 22 16.714 22 12 22C7.28595 22 4.92893 22 3.46447 20.5355C2 19.0711 2 16.714 2 12C2 10.8717 2 9.87835 2.02008 9M12 2C7.28595 2 4.92893 2 3.46447 3.46447C3.03965 3.88929 2.73806 4.38921 2.52396 5" stroke="black" stroke-width="1.5" stroke-linecap="round"/>
+</svg>