feat(i18n): full RTL/CJK support — fonts, Japanese locale, directional fixes

Bundle Noto Sans Arabic + Noto Sans JP (SIL OFL 1.1) as per-glyph fallbacks
for both the UI text theme and every generated PDF, so RTL (Arabic) and CJK
render on all platforms — including desktop, where the system font may lack
them — instead of tofu. A shared pdf_fonts.dart centralizes the PDF theme and
the three label/catalog/recovery services reuse it.

Add Japanese (ja) as the CJK reference locale — fittingly, the app's own name
is Japanese (種, tane, 'seed'). Core strings translated; the rest fall back to
English via slang. Wired into supportedLocales (automatic) and the settings
picker.

Fix three physical Alignment.centerLeft -> AlignmentDirectional.centerStart in
variety_detail_screen, and make month-abbreviation and avatar-initial
truncation grapheme-safe (.characters) so CJK text is never cut mid-character.

Tests: CJK/Arabic PDF glyph render, ja locale resolution + English fallback.
The chat-bubble mirroring flagged by the audit was verified correct (already
respects Directionality) and left unchanged.

apps/app_seeds/lib/i18n/strings_en.g.dart

@@ -424,6 +424,9 @@ class Translations$settings$en {
 	/// en: 'Deutsch'
 	String get langDe => 'Deutsch';
 
+	/// en: '日本語'
+	String get langJa => '日本語';
+
 	/// en: 'About'
 	String get about => 'About';
 
@@ -2598,6 +2601,7 @@ extension on Translations {
 			'settings.langAst' => 'Asturianu',
 			'settings.langFr' => 'Français',
 			'settings.langDe' => 'Deutsch',
+			'settings.langJa' => '日本語',
 			'settings.about' => 'About',
 			'settings.aboutText' => 'Local-first, encrypted inventory for traditional seeds. AGPL-3.0.',
 			'settings.aboutOpen' => 'About Tane',
@@ -3031,9 +3035,9 @@ extension on Translations {
 			'sale.help' => 'Record seed you sold or bought — money, Ğ1, or any currency. A separate model from a gift or a Plantare. No commission is ever taken on seeds.',
 			'sale.add' => 'Record a sale',
 			'sale.empty' => 'No sales yet. Note here what you sell or buy.',
-			'sale.iSold' => 'I sold',
 			_ => null,
 		} ?? switch (path) {
+			'sale.iSold' => 'I sold',
 			'sale.iBought' => 'I bought',
 			'sale.direction' => 'Sold or bought?',
 			'sale.counterparty' => 'With whom?',