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/Security/Bomb Minimalistic.svg

@@ -0,0 +1,7 @@
+<svg width="24" height="24" viewBox="0 0 24 24" fill="none" xmlns="http://www.w3.org/2000/svg">
+<path d="M17 7L15 9" stroke="black" stroke-width="1.5" stroke-linecap="round"/>
+<path d="M19.5 7.5L20.5 8" stroke="black" stroke-width="1.5" stroke-linecap="round"/>
+<path d="M16 3.5L16.5 4.5" stroke="black" stroke-width="1.5" stroke-linecap="round"/>
+<path d="M19 5L20 4" stroke="black" stroke-width="1.5" stroke-linecap="round"/>
+<path d="M5.75 8.00337C6.85315 7.36523 8.13392 7 9.5 7C13.6421 7 17 10.3579 17 14.5C17 18.6421 13.6421 22 9.5 22C5.35786 22 2 18.6421 2 14.5C2 13.1339 2.36523 11.8532 3.00337 10.75" stroke="black" stroke-width="1.5" stroke-linecap="round"/>
+</svg>