gui: Wails v2 vertical MVP — bindings + UI

Go bindings (cmd/verstak-gui/app.go):
- Wire notes.Service, files.Service, actions.Service, worklog.Service
- CreateNote, ListNotes, ReadNote, SaveNote
- ListFiles, ListActions, RunAction
- ListWorklog, CreateWorklog
- Fix DTO mappings for core types

Frontend (frontend/src/):
- api/verstak.js: Wails v2 API wrapper (window.go.main.App)
- App.svelte: full rewrite with sidebar + 6 tabs + notes editor
- Section filtering → nodes by section
- Notes: create, open textarea editor, save, dirty tracking
- Quick actions, worklog entries, empty states
- Node creation modal with section select

Build:
  cd frontend && npm run build
  rm -rf cmd/verstak-gui/frontend-dist && cp -r frontend/dist cmd/verstak-gui/frontend-dist
  go build -tags 'gui production webkit2_41' -o verstak-gui ./cmd/verstak-gui
  ./verstak-gui

cmd/verstak-gui/frontend-dist/assets/index-ClxkTvdE.css

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