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/cmd/exec.go

@@ -446,10 +446,8 @@ func runExec(ctx context.Context, execArgs *executeArgs) func(cmd *cobra.Command
 		config := &runner.Config{
 			Workdir:               execArgs.Workdir(),
 			BindWorkdir:           false,
-			ReuseContainers:       false,
 			ForcePull:             execArgs.forcePull,
 			ForceRebuild:          execArgs.forceRebuild,
-			LogOutput:             true,
 			JSONLogger:            execArgs.jsonLogger,
 			Env:                   env,
 			ProxyEnv:              proxyEnv,
@@ -465,7 +463,6 @@ func runExec(ctx context.Context, execArgs *executeArgs) func(cmd *cobra.Command
 			ContainerCapAdd:       execArgs.containerCapAdd,
 			ContainerCapDrop:      execArgs.containerCapDrop,
 			ContainerOptions:      execArgs.containerOptions,
-			AutoRemove:            true,
 			ArtifactServerPath:    execArgs.artifactServerPath,
 			ArtifactServerPort:    execArgs.artifactServerPort,
 			ArtifactServerAddr:    execArgs.artifactServerAddr,