refactor: remove unreachable runner code (#1179)

Remove inherited act APIs, configuration branches, and test seams that neither the daemon nor exec can reach. Constant-fold settings both entry points already enforce and consolidate duplicate runner paths.

Major removals:

- Unwired custom action-cache and local-repository-cache implementations.
- Legacy matrix, platform, input, container-reuse, logging, Git remote, and action-replacement configuration paths.
- Unused Docker socket, container network, tar-copy, and platform PTY wrappers.
- Single-implementation filesystem, environment, runner, and expression abstractions.
- Duplicated step-container, command-logging, credential, reusable-workflow, and execution paths.
- Generated client mock boilerplate, obsolete fixtures, test-only seams, stale wrappers, and commented-out code.

This removes 2844 net Go lines while retaining Gitea RPC, event, matrix, input, cache, artifact, action, reusable workflow, Docker, host, exec, and release behavior.

Assisted by Codex (GPT-5).

Reviewed-on: https://gitea.com/gitea/runner/pulls/1179
Reviewed-by: bircni <bircni@icloud.com>
Co-authored-by: silverwind <me@silverwind.io>

internal/app/run/runner_idle_cleanup_test.go

@@ -44,7 +44,7 @@ func TestRunnerCleanupStaleTaskDirs(t *testing.T) {
 		now: func() time.Time { return now },
 	}
 
-	r.cleanupStaleTaskDirs(context.Background(), workdirRoot)
+	r.cleanupStaleDirs(context.Background(), workdirRoot, isTaskIDDir)
 
 	assert.NoDirExists(t, oldTask)
 	assert.DirExists(t, freshTask)
@@ -111,7 +111,7 @@ func TestRunnerCleanupStaleTaskDirsMissingRoot(t *testing.T) {
 
 	// Must be a silent no-op rather than a warning or panic when the root
 	// has not yet been created (e.g. the runner has never executed a task).
-	r.cleanupStaleTaskDirs(context.Background(), filepath.Join(t.TempDir(), "missing"))
+	r.cleanupStaleDirs(context.Background(), filepath.Join(t.TempDir(), "missing"), isTaskIDDir)
 }
 
 func TestRunnerCleanupStaleTaskDirsHonorsContext(t *testing.T) {
@@ -135,7 +135,7 @@ func TestRunnerCleanupStaleTaskDirsHonorsContext(t *testing.T) {
 		now: func() time.Time { return now },
 	}
 
-	r.cleanupStaleTaskDirs(ctx, workdirRoot)
+	r.cleanupStaleDirs(ctx, workdirRoot, isTaskIDDir)
 
 	for i := 1001; i <= 1003; i++ {
 		assert.DirExists(t, filepath.Join(workdirRoot, strconv.Itoa(i)))