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/Line Duotone/Home, Furniture/Remote Controller Minimalistic.svg

@@ -0,0 +1,6 @@
+<svg width="24" height="24" viewBox="0 0 24 24" fill="none" xmlns="http://www.w3.org/2000/svg">
+<path opacity="0.5" d="M5 9C5 6.19108 5 4.78661 5.67412 3.77772C5.96596 3.34096 6.34096 2.96596 6.77772 2.67412C7.78661 2 9.19108 2 12 2C14.8089 2 16.2134 2 17.2223 2.67412C17.659 2.96596 18.034 3.34096 18.3259 3.77772C19 4.78661 19 6.19108 19 9V15C19 17.8089 19 19.2134 18.3259 20.2223C18.034 20.659 17.659 21.034 17.2223 21.3259C16.2134 22 14.8089 22 12 22C9.19108 22 7.78661 22 6.77772 21.3259C6.34096 21.034 5.96596 20.659 5.67412 20.2223C5 19.2134 5 17.8089 5 15V9Z" stroke="black" stroke-width="1.5"/>
+<path d="M15 11C15 12.6569 13.6569 14 12 14C10.3431 14 9 12.6569 9 11C9 9.34315 10.3431 8 12 8C13.6569 8 15 9.34315 15 11Z" stroke="black" stroke-width="1.5"/>
+<circle cx="12" cy="5" r="1" fill="black"/>
+<circle cx="12" cy="17" r="1" fill="black"/>
+</svg>