feat: add multi-platform packaging and auto-update infrastructure

- Add PyInstaller configuration (clide.spec) for cross-platform builds
- Add build scripts for macOS (DMG), Linux (AppImage), and Windows (Inno Setup)
- Add Gitea Actions CI/CD workflow for automated releases
- Add auto-update service with Gitea API integration
- Add 'clide update' CLI command for checking and installing updates

Packaging outputs:
- macOS: Signed/notarized .app bundle in DMG
- Linux: Portable AppImage (glibc 2.17+)
- Windows: Inno Setup installer

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

scripts/build-macos.sh

@@ -0,0 +1,101 @@
+#!/bin/bash
+# Build script for macOS distribution
+# Creates a signed and notarized DMG installer
+#
+# Prerequisites:
+#   - Xcode Command Line Tools: xcode-select --install
+#   - create-dmg: brew install create-dmg
+#   - Apple Developer ID certificate installed in Keychain
+#   - Keychain profile for notarytool: xcrun notarytool store-credentials
+#
+# Usage: ./scripts/build-macos.sh [VERSION]
+
+set -e
+
+VERSION="${1:-1.0.0}"
+DEVELOPER_ID="${DEVELOPER_ID:-Developer ID Application: Your Name (TEAMID)}"
+KEYCHAIN_PROFILE="${KEYCHAIN_PROFILE:-AC_PASSWORD}"
+
+echo "========================================"
+echo "Building Clide $VERSION for macOS"
+echo "========================================"
+
+# Ensure we're in the project root
+cd "$(dirname "$0")/.."
+
+# Check for required tools
+if ! command -v create-dmg &> /dev/null; then
+    echo "Error: create-dmg not found. Install with: brew install create-dmg"
+    exit 1
+fi
+
+# Build with PyInstaller
+echo "Building with PyInstaller..."
+pyinstaller clide.spec --clean --noconfirm
+
+# Check if signing is configured
+if [[ "$DEVELOPER_ID" == *"Your Name"* ]]; then
+    echo ""
+    echo "Warning: DEVELOPER_ID not configured. Skipping code signing."
+    echo "To enable signing, set DEVELOPER_ID environment variable."
+    echo ""
+    SKIP_SIGNING=true
+else
+    SKIP_SIGNING=false
+fi
+
+if [[ "$SKIP_SIGNING" == "false" ]]; then
+    # Code sign the app
+    echo "Code signing..."
+    codesign --deep --force --verify --verbose \
+        --sign "$DEVELOPER_ID" \
+        --options runtime \
+        --entitlements packaging/entitlements.plist \
+        --timestamp \
+        "dist/Clide.app"
+
+    # Create ZIP for notarization
+    echo "Creating ZIP for notarization..."
+    ditto -c -k --sequesterRsrc --keepParent \
+        "dist/Clide.app" "dist/Clide-$VERSION.zip"
+
+    # Notarize
+    echo "Submitting for notarization (this may take a few minutes)..."
+    xcrun notarytool submit "dist/Clide-$VERSION.zip" \
+        --keychain-profile "$KEYCHAIN_PROFILE" \
+        --wait
+
+    # Staple the notarization ticket
+    echo "Stapling notarization ticket..."
+    xcrun stapler staple "dist/Clide.app"
+
+    # Clean up ZIP
+    rm "dist/Clide-$VERSION.zip"
+fi
+
+# Create DMG
+echo "Creating DMG..."
+# Remove existing DMG if present
+rm -f "dist/Clide-$VERSION-macos.dmg"
+
+create-dmg \
+    --volname "Clide $VERSION" \
+    --window-pos 200 120 \
+    --window-size 600 400 \
+    --icon-size 100 \
+    --icon "Clide.app" 150 190 \
+    --hide-extension "Clide.app" \
+    --app-drop-link 450 185 \
+    "dist/Clide-$VERSION-macos.dmg" \
+    "dist/Clide.app" || true  # create-dmg returns non-zero even on success sometimes
+
+echo ""
+echo "========================================"
+echo "Build complete!"
+echo "Output: dist/Clide-$VERSION-macos.dmg"
+if [[ "$SKIP_SIGNING" == "true" ]]; then
+    echo ""
+    echo "Note: App was NOT signed or notarized."
+    echo "Users will see Gatekeeper warnings."
+fi
+echo "========================================"