add Eurostat + UK ONS sources; valuation/bubble/economy/bonds groups; aggregate read; market-open header

Three new data sources hooked into the existing SOURCES registry. All
open APIs, no keys:

  - EUROSTAT: prefix EUROSTAT:dataset?dim=val&... — current EU bond
    yields (Bund/OAT/BTP/EZ) and Eurozone economic indicators that
    FRED's OECD-mirror series stopped updating in 2022-2023.
  - ONS: prefix ONS:topic/cdid/dataset — current UK CPI, unemployment,
    GDP, industrial production. Replaces the 5+ month-stale FRED
    LRHUTTTTGBM156S mirror.

New indicator groups in default.toml feed the strategic/fundamental
lens we converged on: valuation (CAPE/Buffett anchors), bubble_watch
(SKEW/VVIX/RSP vs SPY/HYG vs TLT/IPO/crypto), economy (multi-region,
ALL current-or-stale-flagged), bonds (UK/EU/US/JPN sovereign yields).

Indicator panel now opens with an AI "read" interpretation per group
(generated hourly at :07 UTC alongside an aggregate cross-group read
shown in the dashboard header). The aggregate is grounded by a markets
strip — NYSE/LSE/Frankfurt/Tokyo/HK/Shanghai with open/closed LEDs and
next-open countdown, computed locally from each exchange's tz.

Other UX bits: indicator-row tooltips populated from TOML notes;
rows whose last observation is >90 days old get a 'stale' chip;
ghost symbols (in DB but no longer in TOML) filtered out of the
panel; Eurostat/ONS symbols display as short codes rather than the
full API path.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

app/templates/dashboard.html

@@ -2,6 +2,14 @@
 {% block title %}Cassandra · Dashboard{% endblock %}
 
 {% block main %}
+<div id="dash-header-container"
+     style="grid-column: 1 / -1;"
+     hx-get="/api/summary/aggregate?as=html"
+     hx-trigger="load, every 300s"
+     hx-swap="innerHTML">
+  <div class="empty">loading aggregate read…</div>
+</div>
+
 <section id="indicators-panel" class="panel">
   <div class="panel-header">
     <span class="title">Indicators</span>