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/testdata/workflows/capacity.yml

@@ -6,12 +6,12 @@ jobs:
     steps:
       - run: |
           echo "span-start=$(date +%s%N)"
-          sleep 8
+          until curl -fs "${{ vars.E2E_GATE }}" > /dev/null; do sleep 0.1; done
           echo "span-end=$(date +%s%N)"
   two:
     runs-on: e2e-capacity
     steps:
       - run: |
           echo "span-start=$(date +%s%N)"
-          sleep 8
+          until curl -fs "${{ vars.E2E_GATE }}" > /dev/null; do sleep 0.1; done
           echo "span-end=$(date +%s%N)"

e2e/testdata/workflows/cli_shutdown.yml

@@ -6,5 +6,5 @@ jobs:
     steps:
       - run: |
           echo e2e-shutdown-started
-          sleep 8
+          until curl -fs "${{ vars.E2E_GATE }}" > /dev/null; do sleep 0.1; done
           echo e2e-shutdown-finished

e2e/testdata/workflows/failure.yml

@@ -21,10 +21,3 @@ jobs:
     runs-on: ubuntu-latest
     steps:
       - run: echo dependent
-  timeout:
-    runs-on: ubuntu-latest
-    timeout-minutes: 1
-    steps:
-      - run: |
-          echo e2e-timeout-started
-          sleep 300

e2e/testdata/workflows/reconnect.yml

@@ -9,7 +9,10 @@ jobs:
     steps:
       - run: |
           echo e2e-before-outage
-          for i in $(seq -w 1 15); do
+          i=0
+          until curl -fs "${{ vars.E2E_GATE }}" > /dev/null; do
+            i=$((i + 1))
             echo "tick-$i"
-            sleep 1
+            sleep 0.2
           done
+          echo "ticks=$i"

e2e/testdata/workflows/timeout.yml

@@ -0,0 +1,9 @@
+name: timeout
+on: push
+jobs:
+  timeout:
+    runs-on: e2e-timeout
+    steps:
+      - run: |
+          echo e2e-timeout-started
+          sleep 300