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/Weather/Wind.svg

@@ -0,0 +1,5 @@
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+<path d="M3 8H5M7 5.85714V5.5C7 4.11929 8.11929 3 9.5 3C10.8807 3 12 4.11929 12 5.5C12 6.88071 10.8807 8 9.5 8H8" stroke="black" stroke-width="1.5" stroke-linecap="round"/>
+<path d="M4 14H5M15 17V17.5C15 19.433 16.567 21 18.5 21C20.433 21 22 19.433 22 17.5C22 15.567 20.433 14 18.5 14H9" stroke="black" stroke-width="1.5" stroke-linecap="round"/>
+<path d="M2 11H8M15 8V7.5C15 5.567 16.567 4 18.5 4C20.433 4 22 5.567 22 7.5C22 9.433 20.433 11 18.5 11H12.25" stroke="black" stroke-width="1.5" stroke-linecap="round"/>
+</svg>