Add Gantt-style timeline to conference list page

Shows the next 90 days as a horizontal bar chart above the conference
list. A greedy interval-colouring algorithm assigns each conference to a
lane so overlapping conferences appear in separate rows. Lane colour
cycles through a fixed palette so simultaneous events are easy to tell
apart. Month boundary markers and a red today-line provide orientation.
All position maths happens in build_conference_timeline() in Python;
the Jinja template is pure rendering.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

web_view.py

@@ -440,6 +440,73 @@ def _conference_description(conf: StrDict) -> str:
     return "\n".join(lines) if lines else "Conference"
 
 
+def build_conference_timeline(
+    current: list[StrDict], future: list[StrDict], today: date, days: int = 90
+) -> dict | None:
+    """Build data for a Gantt-style timeline of upcoming conferences."""
+    timeline_start = today
+    timeline_end = today + timedelta(days=days)
+
+    visible = [
+        c
+        for c in (current + future)
+        if c["start_date"] <= timeline_end and c["end_date"] >= today
+    ]
+    if not visible:
+        return None
+
+    visible.sort(key=lambda c: c["start_date"])
+
+    # Greedy interval-coloring: assign each conference a lane (row)
+    lane_ends: list[date] = []
+    conf_data = []
+    for conf in visible:
+        lane = next(
+            (i for i, end in enumerate(lane_ends) if end < conf["start_date"]),
+            len(lane_ends),
+        )
+        if lane == len(lane_ends):
+            lane_ends.append(conf["end_date"])
+        else:
+            lane_ends[lane] = conf["end_date"]
+
+        start_off = max((conf["start_date"] - timeline_start).days, 0)
+        end_off = min((conf["end_date"] - timeline_start).days + 1, days)
+        left_pct = round(start_off / days * 100, 2)
+        width_pct = max(round((end_off - start_off) / days * 100, 2), 0.5)
+
+        conf_data.append(
+            {
+                "name": conf["name"],
+                "url": conf.get("url"),
+                "lane": lane,
+                "left_pct": left_pct,
+                "width_pct": width_pct,
+                "label": (
+                    f"{conf['name']}"
+                    f" ({conf['start_date'].strftime('%-d %b')}–"
+                    f"{conf['end_date'].strftime('%-d %b')})"
+                ),
+            }
+        )
+
+    # Month markers for x-axis labels
+    months = []
+    d = today.replace(day=1)
+    while d <= timeline_end:
+        off = max((d - timeline_start).days, 0)
+        months.append({"label": d.strftime("%b %Y"), "left_pct": round(off / days * 100, 2)})
+        # advance to next month
+        d = (d.replace(day=28) + timedelta(days=4)).replace(day=1)
+
+    return {
+        "confs": conf_data,
+        "lane_count": len(lane_ends),
+        "months": months,
+        "days": days,
+    }
+
+
 def build_conference_ical(items: list[StrDict]) -> bytes:
     """Build iCalendar feed for all conferences."""
     lines = [
@@ -488,10 +555,13 @@ def conference_list() -> str:
     ]
     future = [conf for conf in items if conf["start_date"] > today]
 
+    timeline = build_conference_timeline(current, future, today)
+
     return flask.render_template(
         "conference_list.html",
         current=current,
         future=future,
+        timeline=timeline,
         today=today,
         get_country=agenda.get_country,
         fx_rate=agenda.fx.get_rates(app.config),