calendar: consume the scout-calendar feed instead of local events.json

Events now come from EVENTS_FEED_URL (the scout-calendar container,
which serves Radicale mike/site73 as JSON). The last good copy is
cached to /data/events-cache.json and served whenever the feed is down
or empty; 'Nothing on the books' remains the cold-start floor only.
The round-trip test proved the feed reproduces all 32 rows of
app/events.json byte-identically, so nothing visible changes today.

Removes app/events.json, the first-boot seed copy, and the local load
path; README calendar section rewritten; compose gains EVENTS_FEED_URL
from the Portainer stack env.

app/app.py

@@ -1,4 +1,4 @@
-import json, os, shutil, datetime, urllib.request, urllib.parse
+import json, os, time, datetime, urllib.request, urllib.parse
 from pathlib import Path
 from fastapi import FastAPI, Form
 from fastapi.responses import HTMLResponse, RedirectResponse
@@ -11,15 +11,16 @@ import admin_api
 
 # ---------------------------------------------------------------------------
 # Pack & Troop 73 - greenlanescouts73.org
-# Calendar lives in ONE file: /data/events.json (seeded from app/events.json on
-# first boot). Edit that file on the host (or ask Claude) and every page that
-# shows dates updates on the next refresh. No rebuild needed.
+# Calendar comes from the scout-calendar JSON feed (EVENTS_FEED_URL) -
+# Radicale is the source of truth, edited in any calendar app. The last good
+# copy is cached to /data/events-cache.json and served whenever the feed is
+# down, so a feed outage never blanks the site.
 # ---------------------------------------------------------------------------
 
 DATA = Path("/data"); DATA.mkdir(parents=True, exist_ok=True)
 LEADS = DATA / "leads.jsonl"
-EVENTS_LIVE = DATA / "events.json"
-EVENTS_SEED = Path(__file__).parent / "events.json"
+EVENTS_FEED_URL = os.environ.get("EVENTS_FEED_URL", "").strip()
+EVENTS_CACHE = DATA / "events-cache.json"
 NTFY_URL = os.environ.get("NTFY_URL", "")
 # Lead pipeline lives IN THIS REPO (no dependency on the scouting73-form
 # container): direct Google Sheet append + ntfy push, same sheet and topic.
@@ -38,23 +39,55 @@ app.mount("/static", StaticFiles(directory="/app/static"), name="static")
 store.init(backfill_jsonl=LEADS)
 app.include_router(admin_api.router)
 
-if not EVENTS_LIVE.exists() and EVENTS_SEED.exists():
-    try: shutil.copyfile(EVENTS_SEED, EVENTS_LIVE)
-    except Exception: pass
-
 MB = ['JAN','FEB','MAR','APR','MAY','JUN','JUL','AUG','SEP','OCT','NOV','DEC']
 MF = ['January','February','March','April','May','June','July','August','September','October','November','December']
 DW = ['Mon','Tue','Wed','Thu','Fri','Sat','Sun']
 DWU = ['MON','TUE','WED','THU','FRI','SAT','SUN']
 
+_FEED_TTL = 300  # seconds between feed fetches; a failure also waits this long
+_feed_state = {"events": None, "fetched": 0.0}
+
+def _fetch_feed():
+    rq = urllib.request.Request(EVENTS_FEED_URL, headers={"User-Agent": "scout-website"})
+    with urllib.request.urlopen(rq, timeout=5) as resp:
+        events = json.load(resp).get("events", [])
+    if not isinstance(events, list) or not events:
+        raise ValueError("feed returned no events")
+    return events
+
 def load_events():
-    for p in (EVENTS_LIVE, EVENTS_SEED):
+    """Events come from the scout-calendar feed. The last good copy is cached
+    to /data and served whenever the feed is unreachable or empty - the pages
+    never go blank because the feed had a bad moment. With no feed and no
+    cache yet, pages fall back to their 'Nothing on the books' empty state."""
+    now = time.time()
+    st = _feed_state
+    if st["events"] is not None and now - st["fetched"] < _FEED_TTL:
+        return st["events"]
+    if EVENTS_FEED_URL:
         try:
-            with open(p, encoding="utf-8") as f:
-                return json.load(f).get("events", [])
+            events = _fetch_feed()
+            st.update(events=events, fetched=now)
+            try:
+                tmp = EVENTS_CACHE.with_suffix(".tmp")
+                tmp.write_text(json.dumps({"events": events}), encoding="utf-8")
+                tmp.replace(EVENTS_CACHE)
+            except Exception:
+                pass
+            return events
         except Exception:
-            continue
-    return []
+            pass
+    if st["events"] is not None:  # feed down: keep serving stale, retry after TTL
+        st["fetched"] = now
+        return st["events"]
+    try:
+        with open(EVENTS_CACHE, encoding="utf-8") as f:
+            events = json.load(f).get("events", [])
+    except Exception:
+        events = []
+    if events:
+        st.update(events=events, fetched=now)
+    return events
 
 def _dates(ev):
     s = datetime.date.fromisoformat(ev["date"])