feat(config): add pageWidth setting to .remanso.json

Allows repo owners to configure note column width via `"pageWidth": "700px"` in .remanso.json. Applies the value to the --note-width CSS variable and invalidates the cached width so resize/overlay hooks pick it up.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

src/modules/repo/interfaces/UserSettings.ts

@@ -10,4 +10,5 @@ export interface UserSettings extends Model<DataType.UserSettings> {
   backlink?: boolean
   chosenTitleFont?: string
   chosenBodyFont?: string
+  pageWidth?: string
 }