feat(project-editor): finish field descriptions + enum dropdowns across all sections

Wires up the remaining editor sections (theme, header, footer, homepage,
widgets, features, languages, navigation) with the description text and
dropdown UX started for General/Branding:

- Every enum-backed field is now a <select> with a description per option,
  not free text: theme.mode, the new site-wide layout.type (previously had
  no editor at all - added to the Theme section, and added to that
  section's reset-scope), homepage section layout.strategy, and
  catalog.navigationMode (also previously unedited, added to Features).
- Every other field (colors, header toggles, footer contact/company fields,
  widget props, feature flags, language add, nav link label/url/visible)
  gets a one-line plain-language description under its label via the new
  *Desc i18n keys (en/ru/hy) prepared earlier.
- Genuinely open text (widget layout variant strings, JSON props) stays
  free text, description-only, per the existing widgetLayoutDesc/widgetJsonDesc
  wording - not force-fit into a dropdown.

Verified: tsc --noEmit and ng build both clean.

src/app/features/project-editor/models/project-editor.model.ts

@@ -29,7 +29,7 @@ export interface ProjectEditorState {
 export const EDITOR_SECTION_BOOTSTRAP_KEYS: Partial<Record<ProjectEditorSectionId, (keyof BootstrapConfig)[]>> = {
   general: ['tenant', 'seo'],
   branding: ['branding'],
-  theme: ['theme'],
+  theme: ['theme', 'layout'],
   header: ['header'],
   footer: ['footer', 'company'],
   homepage: ['pages'],