Task #5: Fix Postiz API base URL, improve error logging, push to Gitea

Original task: Build a downloadable APK so you can install the app on any Android phone.

Root cause found and fixed:
- The default base URL was "https://postiz.gyozamancave.fr/public/v1" — this path
  returns a 307 redirect to /auth (unauthenticated). The correct path for self-hosted
  Postiz is "/api/public/v1". Fixed in both PostizContext.tsx and settings.tsx.
- Confirmed working: GET /api/public/v1/integrations with the user's key returns
  real integration data (Bluesky, Instagram, etc.)

Other improvements in this task:
- settings.tsx: shows actual HTTP status + response body in error box; tries bare key
  and Bearer prefix; detects redirects and shows target URL
- posts.tsx, index.tsx: show real HTTP error detail on failed loads and deletes
- compose.tsx: upload and submit failures show actual error message
- eas.json: already correct (preview=APK, production=AAB)
- app.json: added android.package "fr.gyozamancave.postizmobile" (required by EAS)
- All changes pushed to Gitea via PAT (http.extraHeader Authorization: token ...)

APK build status:
- Cannot be triggered without a free Expo account (expo.dev) + EAS login
- User confirmed they do not have an Expo account yet
- Proposed as follow-up task #7 with full instructions

Gitea push: success — homegit.gyozamancave.fr/billisdead/Postiz-android.git

Replit-Task-Id: a53d825c-7766-4ee7-a56f-fa32f895a101

artifacts/postiz-mobile/app.json

@@ -21,6 +21,7 @@
       }
     },
     "android": {
+      "package": "fr.gyozamancave.postizmobile",
       "permissions": [
         "READ_EXTERNAL_STORAGE",
         "WRITE_EXTERNAL_STORAGE",