feat: add @automaker/git-utils package

ELIMINATES routes/common.ts: Extract all git operations (382 lines) into dedicated package.

- Extract git status parsing (parseGitStatus, isGitRepo)
- Extract diff generation (generateSyntheticDiffForNewFile, etc.)
- Extract repository analysis (getGitRepositoryDiffs)
- Handle both git repos and non-git directories
- Support binary file detection
- Generate synthetic diffs for untracked files

Split into logical modules:
- types.ts: Constants and interfaces
- status.ts: Git status operations
- diff.ts: Diff generation utilities

This package will replace:
- apps/server/src/routes/common.ts (to be deleted)

Dependencies: @automaker/types, @automaker/utils

🤖 Generated with [Claude Code](https://claude.com/claude-code)

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

libs/git-utils/tsconfig.json

@@ -0,0 +1,20 @@
+{
+  "compilerOptions": {
+    "target": "ES2020",
+    "module": "commonjs",
+    "lib": ["ES2020"],
+    "types": ["node"],
+    "declaration": true,
+    "declarationMap": true,
+    "outDir": "./dist",
+    "rootDir": "./src",
+    "strict": true,
+    "esModuleInterop": true,
+    "skipLibCheck": true,
+    "forceConsistentCasingInFileNames": true,
+    "resolveJsonModule": true,
+    "moduleResolution": "node"
+  },
+  "include": ["src/**/*"],
+  "exclude": ["node_modules", "dist"]
+}