docs: the server runs Gitea 1.27.2, not 1.24.2; say what it actually honours

The CI documentation, the workflow header, the README, ADR 0047 and the
sweep's comment all said the server was Gitea 1.24.2, which ignores
`permissions`, `concurrency` and `timeout-minutes`. The server reports
1.27.2 (GET /api/v1/version).

Each claim is now stated from what is verified on this server:
- `concurrency` is honoured, observed: Ekklesia runs 133 and 135 were
  cancelled when a newer run started for the same pull request;
- `permissions` is supported by 1.27 with Gitea's own scopes, but the
  token's actual authority is not visible through the API and not yet
  proven, so nothing claims the job token is read-only;
- `timeout-minutes` is no longer listed as unsupported, but is not
  verified, and teardown still relies on the stack sweep and a reaper.

Requirement 1 for executing untrusted contributions (upgrade to the
1.26 line or later) is marked done; items 2 and 3, configuring and
proving token authority, remain. ADR 0047 (still Proposed) restates
its "docker run, not a reusable workflow" reasons for 1.27, where
private sources are supported. The reasons still hold without the 1.24
argument.

Co-Authored-By: Claude Opus 5.5 <[email protected]>

.github/workflows/ci.yml

@@ -1,18 +1,13 @@
 name: CI
 
-# IMPORTANT — the currently inventoried server is Gitea 1.24.2, which *ignores* several keys used
-# below. Per https://docs.gitea.com/1.24/usage/actions/comparison, its unsupported workflow syntax
-# includes `permissions` / `jobs.<job_id>.permissions`, `concurrency`, and
-# `jobs.<job_id>.timeout-minutes`. They are declared here deliberately, so the workflow is already
-# correct on a supported release and on GitHub Actions, but on this server they are inert:
+# The server runs Gitea 1.27.2 (docs/development/security.md, "What this server honours"):
 #
-#   * `permissions:` does NOT restrict the in-job `GITEA_TOKEN`. Job-token permission controls,
-#     repository/owner defaults, and server-side maximum-permission clamping arrive in the 1.26
-#     feature line (https://docs.gitea.com/1.26/usage/actions/token-permissions). Until the server
-#     is upgraded and configured, the token's authority is whatever the server grants — not what
-#     this file requests.
-#   * `concurrency:` and `timeout-minutes:` are NOT bounded-execution guarantees here. Cancellation,
-#     timeout, and teardown must be enforced by the trusted runner provisioner/reaper.
+#   * `concurrency:` is honoured: a newer push to a pull request cancels the run it supersedes, so a
+#     cancelled run's own cleanup is never guaranteed (see the CI stack sweep in each stack job).
+#   * `permissions:` is supported by 1.27 with Gitea's own scopes, but what the job token can do on
+#     this server is not yet proven, so nothing here relies on it being read-only.
+#   * `timeout-minutes:` is no longer listed as unsupported, but is not verified here either;
+#     teardown relies on the stack sweep and the runner's own reaper.
 #
 # `persist-credentials: false` below is unaffected by any of this and is enforced by the action
 # itself. See docs/development/security.md.