test(e2e): speed up and cover exec and Kubernetes modes (#1363)

Follow-up to https://gitea.com/gitea/runner/pulls/1362, whose crash e2e missed because it only drove the daemon on Docker.

- `dispatch`, `failure_paths` and `reusable_workflow` run through the daemon and `exec`, each on Docker and one shared k3s cluster.
- Fixed sleeps become gates the test releases, the job timeout uses a 15s runner deadline, k3s boots alongside Gitea, Gitea's data is on tmpfs.
- Outside a container, `make test-e2e` runs `go test` in a Linux container on its own network like CI, so local runs take the same paths.

Local wall time:

| | Before | After |
|---|---|---|
| Suite | 84s | 27–35s |
| `job_timeout` | 64s | 17s |
| `reconnect` | 22s | 4.5s |
| `capacity/serial` | 20s | 2s |
| `cli_shutdown_drains` | 14s | 2.3s |
| `kubernetes` | 31s | 21–23s |

_Written by Claude (Opus 5.5)._

---------

Co-authored-by: bircni <[email protected]>
Reviewed-on: https://gitea.com/gitea/runner/pulls/1363
Reviewed-by: bircni <[email protected]>
Co-authored-by: silverwind <[email protected]>

e2e/compatibility_test.go

@@ -28,19 +28,20 @@ func TestCompatibility(t *testing.T) {
 	t.Run("payloads", testPayloads)
 	t.Run("cache_and_artifacts", testCacheAndArtifactRoundTrips)
 	t.Run("cancellation_and_log_streaming", testRunCancellation)
-	t.Run("dispatch", testWorkflowDispatch)
+	t.Run("dispatch", inAllModes(testWorkflowDispatch))
 	t.Run("builtin_checkout", testBuiltinCheckout)
-	t.Run("exec", testExec)
+	t.Run("exec_artifacts", testExecArtifacts)
 	t.Run("moving_action_ref", testMovingActionRef)
 	t.Run("ephemeral", testEphemeralRunner)
-	t.Run("failure_paths", testFailurePaths)
+	t.Run("failure_paths", inAllModes(testFailurePaths))
+	t.Run("job_timeout", testJobTimeout)
 	t.Run("cli_register_daemon", testCLIRegisterDaemon)
 	t.Run("cli_once", testCLIOnce)
 	t.Run("cli_labels_override", testCLILabelsOverride)
 	t.Run("cli_shutdown_drains", testCLIShutdownDrains)
 	t.Run("cli_shutdown_cancels", testCLIShutdownCancels)
 	t.Run("host_mode", testHostMode)
-	t.Run("reusable_workflow", testReusableWorkflow)
+	t.Run("reusable_workflow", inAllModes(testReusableWorkflow))
 	t.Run("label_routing", testLabelRouting)
 	t.Run("capacity", testCapacity)
 	t.Run("reconnect", testReconnect)