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]>

DEVELOPMENT.md

@@ -57,12 +57,15 @@ Each lives in `internal/pkg/action/<name>` and is registered in `builtinActions`
 
 `make test-e2e` runs the runner against `E2E_GITEA_IMAGE`. It defaults to the nightly image.
 It requires Docker and is excluded from `make test`. CI runs stable and nightly variants in
-parallel.
+parallel. Outside a container it runs `go test` in a Linux container on its own network, as CI does,
+so both take the same paths. `E2E_ARGS` passes extra flags, e.g. `make test-e2e E2E_ARGS='-run TestCompatibility/dispatch'`.
 
 The `cli_*` scenarios build the binary and drive `register` and `daemon` as a user would, including `--once`,
-`--labels` and shutdown with a running job. `failure_paths` covers failed, skipped, tolerated and timed-out jobs.
-`label_routing` and `capacity` cover scheduling, `reconnect` drops the connection to Gitea through a proxy, and
-`host_mode` and `reusable_workflow` cover host labels and `workflow_call`.
+`--labels` and shutdown with a running job. `failure_paths` covers failed, skipped and tolerated jobs, `job_timeout`
+a job killed at the runner's deadline. `label_routing` and `capacity` cover scheduling, `reconnect` drops the
+connection to Gitea through a proxy, and `host_mode` and `reusable_workflow` cover host labels and `workflow_call`.
+`dispatch`, `failure_paths` and `reusable_workflow` run in every mode: through the daemon and `exec`, each on
+Docker and Kubernetes.
 
-The suite shares one Gitea and regular runner. Cache and ephemeral scenarios use isolated
+The suite shares one Gitea, regular runner and k3s cluster. Cache and ephemeral scenarios use isolated
 repository runners. A run path is `<workflow>@<ref>` and a log row is `<timestamp>Z <payload>`.