Pool baseline state across streams sharing an entity concept

Completes the last deferred item from ROADMAP §0: entities recognized as
the same real-world concept across enabled streams (e.g. srcip in both a
firewall and an IIS stream) now share baseline knowledge of entity
presence/age and known relationship-target values, instead of each stream
learning it cold. Implemented additively (synthetic shared_entity:<group>
namespace in the existing baseline.py tables, no schema migration), scoped
to entity presence + relationship known-values only — per-stream
distribution baselines stay untouched. Also fixes a latent alias-map
collision bug found while building this (ALIAS_CANONICAL_BY_FIELD let
"context" silently steal "hostname"/"dns_query" from their own canonical
groups).

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

tests/test_dashboard.py

@@ -99,6 +99,11 @@ class DashboardTests(unittest.TestCase):
         self.assertIn("-entity pattern", HTML)
         self.assertIn("cluster_dampened", HTML)
 
+    def test_dashboard_shows_shared_entity_baselines(self):
+        self.assertIn("shared-entity-baselines", HTML)
+        self.assertIn("Shared Entity Baselines", HTML)
+        self.assertIn("shared_entity_baselines", HTML)
+
     def test_dashboard_shows_shape_mismatch_warnings(self):
         self.assertIn('id="profileShapeWarnings"', HTML)
         self.assertIn("profile_shape_warnings", HTML)