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/Electronic, Devices/Socket.svg

@@ -0,0 +1,8 @@
+<svg width="24" height="24" viewBox="0 0 24 24" fill="none" xmlns="http://www.w3.org/2000/svg">
+<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 7.28595 2 4.92893 3.46447 3.46447C4.92893 2 7.28595 2 12 2C16.714 2 19.0711 2 20.5355 3.46447C21.5093 4.43821 21.8356 5.80655 21.9449 8" stroke="black" stroke-width="1.5" stroke-linecap="round"/>
+<path d="M6.58447 9.41299C6.87047 8.81431 7.2614 8.25323 7.75727 7.75736C10.1004 5.41421 13.8994 5.41421 16.2426 7.75736C18.5857 10.1005 18.5857 13.8995 16.2426 16.2426C13.8994 18.5858 10.1004 18.5858 7.75727 16.2426C7.2614 15.7468 6.87047 15.1857 6.58447 14.587" stroke="black" stroke-width="1.5" stroke-linecap="round"/>
+<path d="M12 18.0001V16.5" stroke="black" stroke-width="1.5" stroke-linecap="round"/>
+<path d="M12 7.5V6" stroke="black" stroke-width="1.5" stroke-linecap="round"/>
+<circle cx="14" cy="12" r="1" fill="black"/>
+<circle cx="10" cy="12" r="1" fill="black"/>
+</svg>