feat(inline-edit): add WYSIWYG inline dashboard editing mode

Replace the disconnected board edit page with inline editing directly
on the board view. Toggle with Ctrl+E or the Edit button. Features:

- Edit mode store with changeset accumulation and batch save
- Floating toolbar (save, discard, add section, board settings, exit)
- Widget hover overlays with edit/delete/drag controls
- Type-specific widget config panels for all 14 widget types
- Section inline editing (title, icon picker, delete)
- "+" buttons for adding widgets and sections inline
- Section-level drag-and-drop reordering via svelte-dnd-action
- Batch save API endpoint (single Prisma transaction)
- Board properties side panel with live theme/wallpaper preview
- Modal widget type picker with search filtering
- Icon picker component with visual grid and search
- Confirmation dialog modal for all destructive actions
- HTML format support for Note widget (in addition to markdown/text)
- Full i18n support (en + ru) for all new UI strings
- Legacy edit page banner linking to new inline mode

plans/inline-dashboard-editing/phase-5-section-editing.md

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+# Phase 5: Section Inline Editing
+
+**Status:** ⬜ Not Started
+**Parent plan:** [PLAN.md](./PLAN.md)
+**Domain:** frontend
+
+## Objective
+Make section headers editable inline in edit mode — title, icon, card size, expand default, delete.
+
+## Tasks
+
+- [ ] Modify `SectionHeader.svelte` to show edit controls when edit mode is active
+- [ ] Pencil icon on section header — click to toggle inline editing of title and icon
+- [ ] Inline title editing: click title text to replace with input field, Enter to confirm, Escape to cancel
+- [ ] Icon picker for section icon (reuse `AppIconPicker` or simplified version)
+- [ ] Card size dropdown override (compact/medium/large/inherit)
+- [ ] Toggle for `isExpandedByDefault`
+- [ ] Delete section button with confirmation ("Delete section 'X' and its N widgets?")
+- [ ] Drag handle for section reordering (left side of header, visible only in edit mode)
+- [ ] All changes stored in edit mode changeset
+
+## Files to Modify/Create
+- `src/lib/components/section/SectionHeader.svelte` — add edit controls
+- `src/lib/components/section/Section.svelte` — pass edit mode state
+- `src/lib/components/section/SectionEditControls.svelte` — new, extracted edit controls
+
+## Acceptance Criteria
+- Section title is editable inline in edit mode
+- Section icon is changeable via picker
+- Card size override works
+- Delete shows confirmation with widget count
+- Changes accumulate in changeset (not persisted until Save)
+- Controls hidden when not in edit mode
+
+## Notes
+- Section drag-and-drop reorder is handled further in Phase 7
+- Delete confirmation should show actual widget count from current state
+
+## Review Checklist
+- [ ] All tasks completed
+- [ ] Code follows project conventions
+- [ ] No unintended side effects
+- [ ] Build passes
+- [ ] Tests pass (new + existing)
+
+## Handoff to Next Phase
+<!-- Filled in after completing this phase -->