chore(ci): disable upptime workflows post-GitHub-suspension (closes part of #2)

All 5 upptime-driven workflows (graphs / response-time / static-site /
summary / uptime) call api.github.com for releases lookup + issue
management + result commits. Post the 2026-05-06 GitHub org
suspension, no token in our org authenticates there anymore — every
scheduled run fails with HTTP 401 "Bad credentials".

Move the workflow files to .github/workflows-disabled/ so Gitea
Actions stops scheduling them. Adds a README explaining what
happened and pointing at #2 for the replacement plan
(Gitea-native uptime probe).

The history/ directory and .upptimerc.yml stay untouched — the
existing probe-list config is still useful as input to the
replacement; the historical JSON files are read-only data we may or
may not migrate forward.

Tracked: #2.

.github/workflows-disabled/README.md

@@ -0,0 +1,19 @@
+# Disabled upptime workflows
+
+These five workflows (`graphs.yml`, `response-time.yml`, `static-site.yml`,
+`summary.yml`, `uptime.yml`) are upptime-driven and call
+`api.github.com` for releases lookup, issue management, and result
+commits.
+
+Post the 2026-05-06 GitHub org suspension, no token in our org
+authenticates against api.github.com, so every scheduled run fails
+with HTTP 401 "Bad credentials". See molecule-ai-status#2 for full
+diagnosis + the replacement plan.
+
+Workflows here will not be re-enabled — they're moved to
+`workflows-disabled/` so the failed-run noise stops while the
+replacement (Gitea-native uptime probe) is built. Delete this
+directory after the replacement lands and the existing history is
+either migrated or marked archived.
+
+Tracked: molecule-ai-status#2