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/Battery Charge Minimalistic.svg

@@ -0,0 +1,5 @@
+<svg width="24" height="24" viewBox="0 0 24 24" fill="none" xmlns="http://www.w3.org/2000/svg">
+<path d="M22 14L22 10" stroke="black" stroke-width="1.5" stroke-linecap="round"/>
+<path d="M11.5 9L9 12H12.5L10 15" stroke="black" stroke-width="1.5" stroke-linecap="round" stroke-linejoin="round"/>
+<path d="M2 12C2 8.22876 2 6.34315 3.17157 5.17157C4.34315 4 6.22876 4 10 4H11.5C15.2712 4 17.1569 4 18.3284 5.17157C19.5 6.34315 19.5 8.22876 19.5 12C19.5 15.7712 19.5 17.6569 18.3284 18.8284C17.1569 20 15.2712 20 11.5 20H10C6.22876 20 4.34315 20 3.17157 18.8284C2.51839 18.1752 2.22937 17.3001 2.10149 16" stroke="black" stroke-width="1.5" stroke-linecap="round"/>
+</svg>