chore: cap every CI job with timeout-minutes (closes #294)

No workflow set timeout-minutes, so a hung build or browser held the
shared runner until the server's own limit, hours later. check now stops
at 10 minutes, e2e-firefox at 15 and e2e-chrome at 20: each is over two
and a half times the job's slowest cold-cache run. README "In CI" records
the measured times and the caps.

Model: opus-5-5

.gitea/workflows/check.yml

@@ -3,6 +3,9 @@ on: [push]
 jobs:
     check:
         runs-on: ubuntu-latest
+        # Bounds script/cibuild, a cold-cache build included, so a hang frees
+        # the shared runner. README.md "In CI" has the measured times.
+        timeout-minutes: 10
         steps:
             # actions/checkout v4.2.2, 2026-02-22
             - uses: actions/checkout@11bd71901bbe5b1630ceea73d27597364c9af683

.gitea/workflows/e2e.yml

@@ -35,6 +35,10 @@ on: [push]
 jobs:
     e2e-chrome:
         runs-on: ubuntu-latest
+        # Bounds the image build, a cold cache included, and both Chrome
+        # programs, so a hung browser frees the shared runner. README.md
+        # "In CI" has the measured times.
+        timeout-minutes: 20
         steps:
             # actions/checkout v4.2.2, 2026-02-22
             - uses: actions/checkout@11bd71901bbe5b1630ceea73d27597364c9af683
@@ -42,6 +46,10 @@ jobs:
 
     e2e-firefox:
         runs-on: ubuntu-latest
+        # Bounds the image build, a cold cache included, and both Firefox
+        # programs, so a hung browser frees the shared runner. README.md
+        # "In CI" has the measured times.
+        timeout-minutes: 15
         steps:
             # actions/checkout v4.2.2, 2026-02-22
             - uses: actions/checkout@11bd71901bbe5b1630ceea73d27597364c9af683