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>

act/runner/command.go

@@ -163,10 +163,6 @@ func (rc *RunContext) setOutput(ctx context.Context, kvPairs map[string]string,
 	logger := common.Logger(ctx)
 	stepID := rc.CurrentStep
 	outputName := kvPairs["name"]
-	if outputMapping, ok := rc.OutputMappings[MappableOutput{StepID: stepID, OutputName: outputName}]; ok {
-		stepID = outputMapping.StepID
-		outputName = outputMapping.OutputName
-	}
 
 	result, ok := rc.StepResults[stepID]
 	if !ok {