ci: run on the desktop runner (runs-on: desktop)

Move jobs from gitdan-ci's ubuntu-latest to the desktop runner label,
the default CI runner per daniel/gitdan#112, and fix comments and docs
that named the old runner.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01MfBCVP2GbKqXSmmJXRPnXP

.gitea/workflows/ci.yaml

@@ -16,7 +16,7 @@ on:
     # cost and the evidence are in README's Development section.
     types: [opened, synchronize, reopened, edited]
 
-# gitdan-ci runs four repos' CI on two capacity slots, and the compiler-backed
+# The desktop runner (gitdan#112) has few slots, and the compiler-backed
 # suites below are multi-minute. A superseded run costs a slot in front of
 # somebody's build, so drop it.
 #
@@ -40,7 +40,7 @@ jobs:
     # no `pull_request` context, so `github.event.pull_request.draft` is empty
     # there and the negation alone would be unreliable. Never drop it.
     if: ${{ github.event_name != 'pull_request' || !github.event.pull_request.draft }}
-    runs-on: ubuntu-latest
+    runs-on: desktop
     timeout-minutes: 20
     # Deliberately no `container.volumes:` entry, unlike every repo that
     # CONSUMES this action. The suites below build throwaway workspaces under
@@ -113,7 +113,7 @@ jobs:
     # job defers or misses.
     needs: selftest
     if: ${{ github.event_name == 'push' && github.ref == 'refs/heads/main' }}
-    runs-on: ubuntu-latest
+    runs-on: desktop
     timeout-minutes: 2
     # Requests write access from the run's built-in token -- whether that
     # grant actually lets it push here is unobserved until the first merge

.gitea/workflows/release-sweep.yaml

@@ -20,7 +20,7 @@ concurrency:
 jobs:
   sweep:
     name: move v1 to main if it lags
-    runs-on: ubuntu-latest
+    runs-on: desktop
     timeout-minutes: 25
     permissions:
       contents: write

README.md

@@ -101,7 +101,7 @@ on:
 
 jobs:
   ci:
-    runs-on: ubuntu-latest
+    runs-on: desktop
     # REQUIRED, and it cannot come from the action: `container.volumes` is a
     # job-level property, so the persistent cache volume must be declared
     # here. Use a volume name unique to this repository.