docs(ci): describe the desktop CI runner, not gitdan-ci

Comment and doc wording only, from the non-blocking findings on daniel/gitdan#114.

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]
 
-# The desktop runner (gitdan#112) has few slots, and the compiler-backed
+# The desktop runner (gitdan#112) has exactly one slot (the `desktop` label, capacity 1), and the compiler-backed
 # suites below are multi-minute. A superseded run costs a slot in front of
 # somebody's build, so drop it.
 #
@@ -47,7 +47,7 @@ jobs:
     # `mktemp -d` and want a cold target dir every time — a persistent cache
     # would make "did this run rebuild?" unanswerable, which is the question
     # restore-mtimes-selftest.sh exists to ask. So this job takes no share of
-    # the shared CI cache disk budget.
+    # the host's shared CI cache disk budget (ci_cache_reclaim).
     steps:
       - name: Checkout sources
         uses: actions/checkout@v4