feat(sync): complete incremental sync protocol with storage-pull, state management, and tests (#799)

- Add storage-pull strategy: rclone-based sync from remote storage with
  overlay and clean modes, URI parsing (storage://remote:bucket/path),
  transfer parallelism, and automatic rclone availability checking
- Add SyncStateManager: persistent state load/save with configurable
  paths, workspace hash calculation via SHA-256 of key project files,
  and drift detection for external modification awareness
- Add action.yml inputs: syncStrategy, syncInputRef, syncStorageRemote,
  syncRevertAfter, syncStatePath with sensible defaults
- Wire sync into Input (5 getters), BuildParameters (5 fields), index.ts
  (local build path), and RemoteClient (orchestrator path) with post-job
  overlay revert when syncRevertAfter is true
- Add 42 unit tests covering all strategies, URI parsing, state
  management, hash calculation, drift detection, error handling, and
  edge cases (missing rclone, invalid URIs, absent state, empty diffs)
- Add root:true to eslintrc to prevent plugin resolution conflicts

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

src/model/build-parameters.ts

@@ -106,6 +106,11 @@ class BuildParameters {
   public cacheUnityInstallationOnMac!: boolean;
   public unityHubVersionOnMac!: string;
   public dockerWorkspacePath!: string;
+  public syncStrategy!: string;
+  public syncInputRef!: string;
+  public syncStorageRemote!: string;
+  public syncRevertAfter!: boolean;
+  public syncStatePath!: string;
 
   public static shouldUseRetainedWorkspaceMode(buildParameters: BuildParameters) {
     return buildParameters.maxRetainedWorkspaces > 0 && Orchestrator.lockedWorkspace !== ``;
@@ -242,6 +247,11 @@ class BuildParameters {
       cacheUnityInstallationOnMac: Input.cacheUnityInstallationOnMac,
       unityHubVersionOnMac: Input.unityHubVersionOnMac,
       dockerWorkspacePath: Input.dockerWorkspacePath,
+      syncStrategy: Input.syncStrategy,
+      syncInputRef: Input.syncInputRef,
+      syncStorageRemote: Input.syncStorageRemote,
+      syncRevertAfter: Input.syncRevertAfter,
+      syncStatePath: Input.syncStatePath,
     };
   }