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

TRANSLATIONS.md

@@ -0,0 +1,87 @@
+# Translating Tane (Weblate)
+
+Runbook for the translation setup. Written so another agent (or a human) can
+reproduce it without prior context.
+
+Tane is translated on **[translate.comunes.org/projects/tane](https://translate.comunes.org/projects/tane/)**
+(a self-hosted **Weblate 5.x**, docker-compose at `/data/weblate` on host **tesla**).
+The links to the repo and to Weblate are shown both on the landing site
+(`site/config.toml` → `sourceURL`, `weblateURL`) and inside the app (About screen).
+
+## What is translatable
+
+| Surface | Files | Format | Base locale | Locales today |
+|---|---|---|---|---|
+| **App** (`app` component) | `apps/app_seeds/lib/i18n/*.i18n.json` | JSON **nested** (slang, `{param}` placeholders) | `en` | en, es, pt, fr, de, ast, ja |
+| **Site** (deferred) | `site/i18n/*.toml` | Hugo TOML | `en` | en, es |
+
+Only source strings live in git; app strings use `slang`, so `strings.g.dart` /
+`strings_*.g.dart` are **generated** (see the slang caveat below).
+
+## Git connection
+
+- Repo: `https://git.comunes.org/comunes/tane.git`, branch **`main`** (private
+  Gitea/Forgejo behind Cloudflare).
+- Weblate must use **HTTPS + an access token** — SSH port 22 is not reachable
+  through Cloudflare, so the stored `Comunes Translations` SSH key is unusable here.
+- Repository URL in Weblate:
+  `https://<user>:<token>@git.comunes.org/comunes/tane.git`
+  where `<token>` is a git.comunes.org access token with **read + write** on
+  `comunes/tane` (Weblate pushes translations back). Generate it in Gitea/Forgejo
+  → Settings → Applications.
+
+## The `app` component (create once)
+
+The `tane` project already exists on Weblate. Add a component (admin UI
+*Add new translation component*, or `docker exec weblate-weblate-1 weblate shell`):
+
+| Field | Value |
+|---|---|
+| Project | `tane` |
+| Name / slug | `app` |
+| Source code repository | `https://<user>:<token>@git.comunes.org/comunes/tane.git` |
+| Repository branch | `main` |
+| File mask | `apps/app_seeds/lib/i18n/*.i18n.json` |
+| Monolingual base language file | `apps/app_seeds/lib/i18n/en.i18n.json` |
+| Template for new translations | `apps/app_seeds/lib/i18n/en.i18n.json` |
+| File format | **JSON nested structure** (`json-nested`) — not flat `json` |
+| Source language | English (`en`) |
+
+Weblate auto-discovers the existing locales from the mask. Leave push-on-commit on
+so translations flow back to `main`.
+
+Sanity check after creating it:
+```sh
+docker exec weblate-weblate-1 weblate shell -c \
+  'from weblate.trans.models import Project; \
+   print(Project.objects.get(slug="tane").component_set.count())'   # expect 1
+```
+Then edit a test string in the UI and confirm a commit lands on
+`git.comunes.org/comunes/tane` (`main`) — that validates the token has write.
+
+## slang regeneration caveat (important)
+
+Weblate only edits the `*.i18n.json` sources. The committed `strings.g.dart` /
+`strings_*.g.dart` are generated and go **stale** on every Weblate commit, and
+there is no CI to regenerate them. Before a release, a maintainer must:
+
+```sh
+git pull
+cd apps/app_seeds && dart run slang     # regenerates strings*.g.dart
+cd ../.. && dart analyze                 # workspace gate
+git add -A && git commit -m "chore(i18n): regenerate slang after Weblate sync"
+```
+
+(Adding a new source string manually? Same steps — edit `en.i18n.json` first, then
+regenerate. `fallback_strategy: base_locale` means locales missing a key show the
+English text until translators fill it in.)
+
+## Site component — deferred
+
+Weblate 5.x has no native Hugo-TOML format, and the site has only EN/ES (~3 KB).
+Two options, decide later:
+- (a) Switch Hugo i18n to a Weblate-supported format (Hugo also reads
+  `i18n/*.json` / `*.yaml`), then add a matching `site` component.
+- (b) Keep translating the two `site/i18n/*.toml` files by hand.
+
+For now the site is translated manually; only the `app` component is on Weblate.