perf: move SwiftData cache and JSON encode off main thread during sync

- cacheStories() runs in Task.detached with a background ModelContext
- persistQuickCache() encodes 100 stories off-thread via Task.detached
- loadSectionSupplements() batches 5 parallel fetches into one sectionSupplement write

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

.github/workflows/ci.yml

@@ -1,14 +1,15 @@
-# Gitea Actions reads this path (.github/workflows) as well as .gitea/workflows.
-# iOS builds require a macOS runner: register a Gitea act_runner on a Mac with
-# labels matching `runs-on` below (macos-14 / macos-15), or change them to your
-# runner's label. On GitHub-hosted runners these labels work as-is.
+# Gitea Actions reads .github/workflows/ (as well as .gitea/workflows/).
+# Keeping everything here avoids running two duplicate pipelines.
+#
+# Runner requirement: a Mac with Xcode 16+ registered as a Gitea act_runner
+# with labels "self-hosted" and "macos" (see CONTRIBUTING.md → Runner Setup).
 name: CI
 
 on:
-  push:
-    branches: [ main ]
   pull_request:
-    branches: [ main ]
+    branches: [main, develop]
+  push:
+    branches: [develop]
 
 concurrency:
   group: ci-${{ github.ref }}
@@ -16,13 +17,12 @@ concurrency:
 
 jobs:
   build:
-    name: Build · ${{ matrix.os }} · ${{ matrix.configuration }}
-    runs-on: ${{ matrix.os }}
+    name: Build · ${{ matrix.configuration }}
+    runs-on: [self-hosted, macos]
     strategy:
       fail-fast: false
       matrix:
-        os: [ macos-14, macos-15 ]
-        configuration: [ Debug, Release ]
+        configuration: [Debug, Release]
 
     steps:
       - uses: actions/checkout@v4
@@ -31,7 +31,7 @@ jobs:
         run: xcodebuild -version
 
       - name: Install XcodeGen
-        run: brew install xcodegen
+        run: brew list xcodegen &>/dev/null || brew install xcodegen
 
       - name: Generate Xcode project
         run: xcodegen generate
@@ -49,3 +49,20 @@ jobs:
             CODE_SIGNING_ALLOWED=NO \
             CODE_SIGNING_REQUIRED=NO \
             build
+
+      # Compiles the test bundle. No test targets exist yet (see docs/BACKLOG.md #13).
+      # Replace with `xcodebuild test` once a JarvisTests target is added to project.yml.
+      - name: Build for Testing (Debug)
+        if: matrix.configuration == 'Debug'
+        run: |
+          set -o pipefail
+          xcodebuild \
+            -project Jarvis.xcodeproj \
+            -scheme Jarvis \
+            -configuration Debug \
+            -sdk iphonesimulator \
+            -destination 'platform=iOS Simulator,OS=latest,name=iPhone 16' \
+            -derivedDataPath build \
+            CODE_SIGNING_ALLOWED=NO \
+            CODE_SIGNING_REQUIRED=NO \
+            build-for-testing