Replace Checkout action with Cache action for build file caching

Convert the composite action from Checkout to Cache that:
- Stores build files under ~/.cache/ by default
- Auto-generates cache keys from lockfile hashes
- Uses actions/cache@v5 for restore and save
- Supports custom path, key, key-file, and restore-keys inputs
- Exposes cache-hit output for conditional workflow steps

README.md

@@ -1,2 +1,124 @@
-# Cache
+Cache Action
+============
 
+A Gitea Action that caches build files under `~/.cache/` using a key file hash. This action uses `actions/cache@v5` under the hood and automatically saves the cache when the job completes successfully.
+
+## Inputs
+
+| Input | Description | Required | Default |
+|-------|-------------|----------|---------|
+| `path` | Files/directories to cache | No | `~/.cache/` |
+| `key` | Explicit cache key | No | Auto-generated from hash |
+| `key-file` | File to hash for cache key generation | No | Auto-detects lockfiles |
+| `restore-keys` | Fallback prefix-matched keys | No | `{os}-cache-` |
+
+## Outputs
+
+| Output | Description |
+|--------|-------------|
+| `cache-hit` | `true` if exact key match found, `false` otherwise |
+
+## Quick Start
+
+### Basic Usage
+
+```yaml
+name: Build with Cache
+on: push
+
+jobs:
+  build:
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v4
+      - uses: Actions/Cache@main
+      - run: echo "Cache restored, proceeding with build..."
+```
+
+### With Custom Key File
+
+```yaml
+name: Build with Cache
+on: push
+
+jobs:
+  build:
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v4
+      - uses: Actions/Cache@main
+        with:
+          key-file: 'package-lock.json'
+      - run: npm ci
+      - run: npm run build
+```
+
+### .NET Example
+
+```yaml
+name: .NET Build
+on: push
+
+defaults:
+  run:
+    shell: bash
+
+jobs:
+  build:
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v4
+      - uses: Actions/Cache@main
+        with:
+          key-file: '**/*.csproj'
+          path: |
+            ~/.cache/
+            ~/.nuget/packages
+      - name: Build
+        working-directory: src/
+        run: |
+          dotnet restore
+          dotnet build --no-restore -c Release
+          dotnet publish --no-build -c Release
+```
+
+### Skip Steps on Cache Hit
+
+```yaml
+name: Build with Conditional Steps
+on: push
+
+jobs:
+  build:
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v4
+      - uses: Actions/Cache@main
+        id: cache
+        with:
+          key-file: 'requirements.txt'
+      - name: Install dependencies
+        if: steps.cache.outputs.cache-hit != 'true'
+        run: pip install -r requirements.txt
+```
+
+## How It Works
+
+1. **Cache Key Generation**: If no explicit `key` is provided, the action auto-generates one by:
+   - Hashing the specified `key-file` if provided
+   - Otherwise, hashing all detected lockfiles (package-lock.json, Cargo.lock, go.mod, etc.)
+   - Falls back to hashing all non-git files if no lockfiles found
+
+2. **Cache Restore**: Uses `actions/cache@v5` to restore the cache from `~/.cache/`
+
+3. **Cache Save**: Automatically saves the cache when the job completes successfully (handled by `actions/cache@v5`)
+
+## Cache Scope
+
+The cache is scoped to the key, version, and branch. The default branch cache is available to other branches.
+
+## Remarks
+
+- Requires Gitea Actions runner version >= 2.327.1 for `actions/cache@v5`
+- The cache server must be enabled on your Gitea instance
+- Maximum cache size per repository is 10GB