Surface stale deadlines instead of showing them as upcoming

The calendar's deadline table rendered every recorded submission cycle, so
elapsed rounds sorted to the top and read as the next thing due — 13 of its 17
rows were already in the past. Underneath that, the fetcher preserves
`source: manual` entries forever without ever checking whether they still
describe a future deadline, and 11 of 13 cloud-edge venues are manual.

Preserving them is correct: WikiCFP cannot express multi-cycle venues and does
not carry most systems conferences at all, so re-fetching would replace
researched rounds with worse data or nothing. What was missing is a signal.

- Extract the cycle helpers into cycles.py so the fetcher and the generator
  share one definition of which round a reader should act on. cycles_of()
  reads an entry without folding flat fields into a cycles list, which would
  otherwise rewrite every single-round entry the fetcher writes back.
- The calendar table lists open cycles only; a venue whose every round has
  elapsed moves to an "Awaiting the next call" table instead of vanishing.
- pa-fetch-deadlines records those venues under a new stale: key and probes
  the year-bumped CFP URL to say which ones already have a next edition
  online. A candidate must return 200, mention the target year, and be newer
  than any year the entry records — venues.yaml still points SC at sc24.
- README: Task 7 and a matching agent prompt for keeping deadlines current,
  since nothing in this repo refreshes them on its own.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

site/data/cloud-edge/deadlines.yaml

@@ -1,4 +1,4 @@
-generated: '2026-08-17T16:18:08Z'
+generated: '2026-08-17T20:21:42Z'
 deadlines:
   EuroSys:
     source: manual
@@ -115,6 +115,15 @@ deadlines:
     notification: Feb 10, 2026
     camera_ready: Mar 15, 2026
     cfp_url: https://ccgrid2026.org/cfp.html
+  IPDPS:
+    source: manual
+    event_dates: Jun 1-5, 2027
+    location: Seattle, WA, USA
+    abstract_deadline: Oct 1, 2026
+    submission_deadline: Oct 8, 2026
+    notification: Feb 2, 2027
+    camera_ready: Feb 20, 2027
+    cfp_url: https://www.ipdps.org/ipdps2027/2027-call-for-papers.html
   SOSP:
     wikicfp_event_id: '191399'
     source: wikicfp
@@ -126,15 +135,6 @@ deadlines:
     camera_ready: Aug 28, 2026
     cfp_url: https://sigops.org/s/conferences/sosp/2026/cfp.html
     wikicfp_title: SOSP
-  IPDPS:
-    source: manual
-    event_dates: Jun 1-5, 2027
-    location: Seattle, WA, USA
-    abstract_deadline: Oct 1, 2026
-    submission_deadline: Oct 8, 2026
-    notification: Feb 2, 2027
-    camera_ready: Feb 20, 2027
-    cfp_url: https://www.ipdps.org/ipdps2027/2027-call-for-papers.html
   HPDC:
     wikicfp_event_id: '191029'
     source: wikicfp
@@ -147,3 +147,40 @@ deadlines:
     cfp_url: https://hpdc.sci.utah.edu/2026/calls-cfp.html
     wikicfp_title: HPDC
 missing: []
+stale:
+- acronym: ATC
+  last_deadline: Jun 10, 2026
+  source: manual
+  cfp_url: https://sigops.org/s/conferences/atc/2026/cfp.html
+- acronym: CCGrid
+  last_deadline: Dec 21, 2025
+  source: manual
+  cfp_url: https://ccgrid2026.org/cfp.html
+- acronym: HPDC
+  last_deadline: Feb 5, 2026
+  source: wikicfp
+  cfp_url: https://hpdc.sci.utah.edu/2026/calls-cfp.html
+- acronym: Middleware
+  last_deadline: Jun 5, 2026
+  source: manual
+  cfp_url: https://middleware-conf.github.io/2026/calls/call-for-research-papers/
+- acronym: MobiSys
+  last_deadline: Dec 5, 2025
+  source: manual
+  cfp_url: https://www.sigmobile.org/mobisys/2026/
+- acronym: SC
+  last_deadline: Apr 8, 2026
+  source: manual
+  cfp_url: https://sc26.supercomputing.org/program/papers/
+- acronym: SEC
+  last_deadline: May 8, 2026
+  source: manual
+  cfp_url: https://acm-ieee-sec.org/2026/
+- acronym: SOSP
+  last_deadline: Apr 1, 2026
+  source: wikicfp
+  cfp_url: https://sigops.org/s/conferences/sosp/2026/cfp.html
+- acronym: SoCC
+  last_deadline: Jul 14, 2026
+  source: manual
+  cfp_url: https://acmsocc.org/2026/papers.html