TP-F3 — Visual theme editor in Preferences

[ZhuchkaTriplesix]

Epic: #159
Depends on: TP-21 (Preferences integration), TP-08 (QueryaTheme factory), shipped in 0.4.2

Source: docs/planned-0.4.3.md

Goal

Let users tweak a subset of theme colors in Preferences → Appearance and export the result as a valid querya.theme.v1 JSON file (MVP: export-only; saving directly to themes folder can be a follow-up).

Files

• lib/features/settings/... (new editor section/widget)
• lib/core/theme/parser/querya_theme_manifest.dart (serialization helper)
• lib/core/theme/theme_controller.dart (apply preview from edited manifest)
• docs/theme-custom-json.md
• widget tests under test/features/settings/

Implementation (MVP scope)

• Start from the currently selected registry theme or a blank dark/light template.
• Editable groups (first pass):
  • shadcn_colors: primary, background, foreground, card, border
  • editor_colors: background, foreground, selection
  • workbench_colors: canvas, sidebar, titleBar (subset)
• Color picker using existing design system; live preview via ThemeController without rewriting entire app state on every keystroke (debounce).
• Export… action: save dialog → write querya.theme.v1 JSON with generated id if missing.
• Validate colors through existing parseQueryaThemeColor pipeline before export.

Acceptance Criteria

• User can change at least the MVP color set and see preview update in Preferences.
• Exported JSON validates against schema and can be re-imported via Import theme….
• Export does not corrupt unrelated manifest fields from the source theme.
• Editor is disabled / shows message when built-in read-only themes cannot be edited in place (export as copy instead).

Tests

• Widget test: change primary → preview callback invoked.
• Unit test: export produces parseable manifest round-trip.

Notes

If scope grows, split save to themes folder and tokenColors editor to a later issue / 0.4.4.

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