feat(extension): implement Code Wiki button for GitHub repositories

Add browser extension that injects a Code Wiki button into GitHub repository pages,
allowing users to quickly navigate to Google's Code Wiki documentation platform.

Features:
- Chrome extension with Manifest v3 support
- Automatic button injection on GitHub repository pages
- Code Wiki URL format: https://codewiki.google/github.com/{owner}/{repo}
- Multi-language support (14 languages)
- SPA navigation handling with MutationObserver
- Cross-browser compatibility (Chrome, Firefox, Edge)

Technical implementation:
- TypeScript-based content script and background service worker
- Icon generation pipeline using Sharp
- Biome for code linting and formatting
- Secretlint for security scanning

Infrastructure:
- GitHub Actions workflows for automated builds
- Renovate bot for dependency updates
- Sponsor configuration for GitHub Sponsors

Structure:
- app/: Extension source code (manifest, scripts, styles, locales, images)
- .github/: CI/CD workflows and bot configurations
- scripts/: Build utilities
- promo/: Promotional assets directory

Closes #N/A

Author: yamadashy

.editorconfig

@@ -0,0 +1,13 @@
+root = true
+
+[*]
+indent_style = space
+indent_size = 2
+charset = utf-8
+trim_trailing_whitespace = true
+insert_final_newline = true
+end_of_line = lf
+max_line_length = unset
+
+[*.md]
+trim_trailing_whitespace = false

.github/FUNDING.yml

@@ -0,0 +1 @@
+github: yamadashy

.github/renovate.json5

@@ -0,0 +1,21 @@
+{
+  "$schema": "https://docs.renovatebot.com/renovate-schema.json",
+  "extends": [
+    "config:recommended",
+    "schedule:weekly",
+    'group:allNonMajor'
+  ],
+  "rangeStrategy": "bump",
+  "dependencyDashboard": false,
+  "labels": ["dependencies", "renovate"],
+  "automerge": true,
+  "packageRules": [
+    {
+      matchDepTypes: ['peerDependencies'],
+      enabled: false,
+    },
+  ],
+  "ignoreDeps": [
+    "node",
+  ]
+}

.github/workflows/build.yml

@@ -0,0 +1,43 @@
+name: Build Extensions
+
+on:
+  push:
+    branches: [ main ]
+  pull_request:
+    branches: [ main ]
+  workflow_dispatch:
+
+jobs:
+
+  build:
+    runs-on: ubuntu-24.04
+    timeout-minutes: 20
+    steps:
+    - name: Checkout code
+      uses: actions/checkout@v4
+      with:
+        lfs: true
+
+    - name: Setup node
+      uses: actions/setup-node@v4
+      with:
+        node-version-file: .node-version
+        cache: npm
+
+    - name: Install dependencies
+      run: npm ci
+
+    - name: Build Chrome Extension
+      run: npm run build chrome
+
+    - name: Build Firefox Extension
+      run: npm run build firefox
+
+    - name: Build Edge Extension
+      run: npm run build edge
+
+    - name: Archive packages
+      uses: actions/upload-artifact@v4
+      with:
+        name: packages
+        path: packages

.github/workflows/repomix.yml

@@ -0,0 +1,27 @@
+name: Pack repository with Repomix
+
+on:
+  workflow_dispatch:
+  push:
+    branches: [ main ]
+  pull_request:
+    branches: [ main ]
+
+jobs:
+  pack-repo:
+    runs-on: ubuntu-latest
+    steps:
+      - name: Checkout code
+        uses: actions/checkout@v4
+
+      - name: Pack repository with Repomix
+        uses: yamadashy/repomix/.github/actions/repomix@main
+        with:
+          output: repomix-output.xml
+
+      - name: Upload Repomix output
+        uses: actions/upload-artifact@v4
+        with:
+          name: repomix-output.xml
+          path: repomix-output.xml
+          retention-days: 30