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/Essentional, UI/Share.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="M4 12C4 13.3807 5.11929 14.5 6.5 14.5C7.88071 14.5 9 13.3807 9 12C9 10.6193 7.88071 9.5 6.5 9.5" stroke="black" stroke-width="1.5" stroke-linecap="round"/>
+<path d="M14 6.5L9 10" stroke="black" stroke-width="1.5" stroke-linecap="round"/>
+<path d="M14 17.5L9 14" stroke="black" stroke-width="1.5" stroke-linecap="round"/>
+<path d="M16.5 21C17.8807 21 19 19.8807 19 18.5C19 17.1193 17.8807 16 16.5 16C15.1193 16 14 17.1193 14 18.5" stroke="black" stroke-width="1.5" stroke-linecap="round"/>
+<path d="M18.665 6.74999C17.9746 7.94572 16.4457 8.35541 15.2499 7.66505C14.0542 6.9747 13.6445 5.44572 14.3349 4.24999C15.0252 3.05426 16.5542 2.64457 17.7499 3.33493" stroke="black" stroke-width="1.5" stroke-linecap="round"/>
+</svg>