ci: add Gitea Actions CI/CD, branch workflow, and contributor docs

- .gitea/workflows/ci.yml: build + test KisaniCal scheme on a self-hosted
  macOS runner for every PR into main/develop (and pushes to develop).
- .gitea/workflows/release.yml: archive + export IPA on push to main, with
  a commented TestFlight upload placeholder (App Store Connect API key).
- ExportOptions.plist: export template (Team ID K8BLMMR883, app-store method).
- scripts/gitea-setup.sh: idempotent Gitea API setup for develop default
  branch + main branch protection.
- CONTRIBUTING.md: feature/* -> develop -> main workflow and PR gate rules.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

.gitea/workflows/ci.yml

@@ -0,0 +1,86 @@
+name: CI
+
+# Build + test on every PR into main or develop (and on direct pushes to develop).
+on:
+  pull_request:
+    branches: [main, develop]
+  push:
+    branches: [develop]
+
+# ⚠️ RUNNER LABELS — must match how your Mac runner was registered with act_runner.
+#    Check your runner's labels in Gitea: Settings → Actions → Runners (click the runner).
+#    If it registered as e.g. `macos` or `self-hosted`, change `runs-on` below to match.
+#    `[self-hosted, macOS]` means "a runner that has BOTH labels".
+jobs:
+  build-and-test:
+    runs-on: [self-hosted, macOS]
+
+    env:
+      SCHEME: KisaniCal
+      PROJECT: KisaniCal.xcodeproj
+
+    steps:
+      - name: Checkout
+        uses: actions/checkout@v4
+
+      # The .xcodeproj is generated from project.yml via XcodeGen.
+      # Regenerate it so CI never builds a stale project. No-op if xcodegen isn't installed.
+      - name: Regenerate Xcode project (XcodeGen)
+        run: |
+          if command -v xcodegen >/dev/null 2>&1; then
+            xcodegen generate
+          else
+            echo "xcodegen not found on runner — using committed ${PROJECT}."
+            echo "Install with: brew install xcodegen"
+          fi
+
+      - name: Show toolchain
+        run: |
+          xcodebuild -version
+          xcrun simctl list runtimes | grep -i ios || true
+
+      # Pick a concrete, bootable iOS Simulator (needed for `xcodebuild test`).
+      - name: Select iOS Simulator destination
+        id: sim
+        run: |
+          # First available iPhone simulator on any installed iOS runtime.
+          UDID=$(xcrun simctl list devices available -j | python3 -c "import json,sys,re; d=json.load(sys.stdin)['devices']; devs=[x for k,v in d.items() if re.search('iOS',k) for x in v if x.get('isAvailable') and 'iPhone' in x['name']]; print(devs[0]['udid'] if devs else '')")
+          if [ -z "$UDID" ]; then
+            echo "No available iPhone simulator found on the runner." >&2
+            echo "Install an iOS runtime via Xcode → Settings → Components." >&2
+            exit 1
+          fi
+          echo "udid=$UDID" >> "$GITHUB_OUTPUT"
+          echo "Using simulator UDID: $UDID"
+
+      - name: Build
+        run: |
+          set -o pipefail
+          xcodebuild build \
+            -project "$PROJECT" \
+            -scheme "$SCHEME" \
+            -configuration Debug \
+            -destination "id=${{ steps.sim.outputs.udid }}" \
+            CODE_SIGNING_ALLOWED=NO \
+            | xcbeautify || xcodebuild build \
+            -project "$PROJECT" \
+            -scheme "$SCHEME" \
+            -configuration Debug \
+            -destination "id=${{ steps.sim.outputs.udid }}" \
+            CODE_SIGNING_ALLOWED=NO
+
+      - name: Test
+        run: |
+          set -o pipefail
+          xcodebuild test \
+            -project "$PROJECT" \
+            -scheme "$SCHEME" \
+            -configuration Debug \
+            -destination "id=${{ steps.sim.outputs.udid }}" \
+            CODE_SIGNING_ALLOWED=NO \
+            | xcbeautify || xcodebuild test \
+            -project "$PROJECT" \
+            -scheme "$SCHEME" \
+            -configuration Debug \
+            -destination "id=${{ steps.sim.outputs.udid }}" \
+            CODE_SIGNING_ALLOWED=NO