feat: custom font loading pipeline + Mac Retina fix (v0.1.23)

[kolkov]

Summary

• Custom font loading pipeline (TASK-UI-CJK-001, gg#304) — plugins load CJK/custom fonts via LoadFont(), auto-registered in global FontRegistry
• FontRegistry — process-global singleton, thread-safe (RWMutex), CSS weight matching, Inter fallback, *text.FontSource caching
• StyledTextDrawer optional interface — DrawStyledText + MeasureStyledText on Canvas and SceneCanvas
• TextWidget.FontFamily() — builder method routes to custom font when available
• Plugin → Registry wiring — MemoryAssetLoader.LoadFont() auto-registers in GlobalFontRegistry()
• Mac Retina fix — gg v0.46.9, MarkDirty() logical→physical pixel dimensions (gg#308, @sverrehu)
• CJK IsCJK propagation — gg v0.46.8, ShapedGlyph.IsCJK through scene/shaper paths (gg#304)
• 47 new tests, ARCHITECTURE.md + ROADMAP.md updated

Architecture

Follows universal pattern from Flutter (FontCollection), Qt6 (QFontDatabase), Iced (FontSystem):

1. Global font registry (process-singleton, RWMutex)
2. Resolution chain: widget font → CSS weight match → Inter fallback
3. Widgets hold family name string, not font data
4. FontSource created once at registration, cached

Test plan

• go build ./...
• go test ./... -count=1 (56 packages, 0 failures)
• golangci-lint run --timeout=5m (0 issues)
• Visual verification: IDE example renders correctly, no regressions
• CI green on all platforms

[codecov]

Codecov Report

❌ Patch coverage is 85.00000% with 27 lines in your changes missing coverage. Please review.

Files with missing lines	Patch %	Lines
internal/render/fontregistry.go	88.33%	4 Missing and 3 partials ⚠️
internal/render/scene_canvas.go	84.09%	4 Missing and 3 partials ⚠️
uitest/canvas.go	25.00%	6 Missing ⚠️
internal/render/canvas.go	88.23%	2 Missing and 2 partials ⚠️
plugin/context.go	70.00%	2 Missing and 1 partial ⚠️

📢 Thoughts on this report? Let us know!