ci: use self-hosted runner label for iOS and Android builds

Allow builds to run on any available self-hosted runner (mini or studio)
instead of requiring a specific runner.

Also add backlog task for future Android build optimizations.

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

Author: pythoninthegrass

.github/workflows/build-android-app.yml

@@ -29,7 +29,7 @@ concurrency:
 
 jobs:
   build:
-    runs-on: mini
+    runs-on: self-hosted
     env:
       BUNDLE_FROZEN: "true"
       RUBYOPT: "-W0"

.github/workflows/build-ios-app.yml

@@ -29,7 +29,7 @@ concurrency:
 
 jobs:
   build:
-    runs-on: mini
+    runs-on: self-hosted
     env:
       BUNDLE_FROZEN: "true"
       RUBYOPT: "-W0"

backlog/tasks/task-035 - Optimize-Android-CI-build-time.md

@@ -0,0 +1,31 @@
+---
+id: task-035
+title: Optimize Android CI build time
+status: To Do
+assignee: []
+created_date: '2026-02-04 20:47'
+labels:
+  - ci
+  - android
+  - performance
+dependencies: []
+priority: medium
+---
+
+## Description
+
+<!-- SECTION:DESCRIPTION:BEGIN -->
+Android CI builds take ~8 minutes compared to iOS's ~2 minutes. Two optimizations can significantly reduce this:
+
+1. **Cache Rust target directories**: Add Android Rust target directories to the GitHub Actions cache. Currently only `src-tauri/gen/android/app/build` is cached, but the Rust compilation artifacts in `src-tauri/target/*-linux-android*` are rebuilt from scratch each run.
+
+2. **Reduce target architectures**: Build only arm64 and armv7, dropping i686 and x86_64. Most modern Android devices are arm64, and armv7 covers older devices. The x86/x64 targets are primarily for emulators and rare Chrome OS devices.
+<!-- SECTION:DESCRIPTION:END -->
+
+## Acceptance Criteria
+<!-- AC:BEGIN -->
+- [ ] #1 Android Rust target directories are included in GHA cache
+- [ ] #2 Android builds target only aarch64-linux-android and armv7-linux-androideabi
+- [ ] #3 i686-linux-android and x86_64-linux-android targets are removed from CI builds
+- [ ] #4 Android CI build time is reduced (target: under 5 minutes)
+<!-- AC:END -->