feat(links): surface source repo + Weblate links on site and in app

- site: set sourceURL (git.comunes.org/comunes/tane) and weblateURL
  (translate.comunes.org/projects/tane) — activates footer + collaborate links
- app About screen: add 'Source code' and 'Help translate' link tiles
- i18n: add about.sourceCode / about.translate / about.translateSubtitle
  (en base + es/pt/fr/de/ast; ja falls back to base), regenerate slang
- docs: add TRANSLATIONS.md runbook for the Weblate app component + git
  token + slang-regeneration workflow

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

@@ -577,6 +577,15 @@ class Translations$about$en {
 	/// en: 'Website'
 	String get website => 'Website';
 
+	/// en: 'Source code'
+	String get sourceCode => 'Source code';
+
+	/// en: 'Help translate'
+	String get translate => 'Help translate';
+
+	/// en: 'Help bring Tane to your language'
+	String get translateSubtitle => 'Help bring Tane to your language';
+
 	/// en: 'Open-source licenses'
 	String get openSourceLicenses => 'Open-source licenses';
 
@@ -2721,6 +2730,9 @@ extension on Translations {
 			'about.license' => 'License',
 			'about.licenseValue' => 'AGPL-3.0',
 			'about.website' => 'Website',
+			'about.sourceCode' => 'Source code',
+			'about.translate' => 'Help translate',
+			'about.translateSubtitle' => 'Help bring Tane to your language',
 			'about.openSourceLicenses' => 'Open-source licenses',
 			'about.openSourceLicensesSubtitle' => 'Third-party libraries and their licenses',
 			'about.copyright' => ({required Object years}) => '© ${years} Comunes Association, under AGPLv3',
@@ -3107,11 +3119,11 @@ extension on Translations {
 			'plantare.returnSimilar' => 'A similar amount of seed',
 			'plantare.returnSimilarNote' => 'open-pollinated · non-GMO · organically grown',
 			'plantare.returnWork' => 'Some hours of work',
+			_ => null,
+		} ?? switch (path) {
 			'plantare.returnOther' => 'Something else',
 			'plantare.workHoursLabel' => 'How many hours?',
 			'plantare.proposalsSection' => 'Waiting for your reply',
-			_ => null,
-		} ?? switch (path) {
 			'plantare.incomingFrom' => ({required Object name}) => '${name} proposes a Plantaré',
 			'plantare.accept' => 'Accept & sign',
 			'plantare.declineAction' => 'Decline',