knowledge: entity-graph endpoint for force-directed view

New GET /knowledge/graph?type=&limit= returns the data the
curation UI's graph tab needs:
  - nodes = entities with at least one in-scope fact (rejected /
    superseded excluded). Carries fact_count for visual sizing.
    Top-N by count desc; default cap 200 (clamped 1..1000).
  - edges = relational facts (object_entity_id set) grouped by
    (subject, object, predicate) so 3 "is_friend_of" facts
    between the same pair collapse into one edge with count=3.

Two raw SQL queries: an INNER JOIN onto a persona-scoped fact-
count subquery for nodes (skips 0-fact entities entirely so the
sim doesn't waste time on disconnected islands), then a follow-
up GROUP BY over the persona-scoped fact set restricted to the
node id set via IN clauses (ids are i32 so inlining is safe).

Pairs with the Apollo-side GraphPanel that runs d3-force over
the returned payload and renders SVG with click-to-open.

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

src/database/mod.rs

@@ -59,8 +59,8 @@ pub use calendar_dao::{CalendarEventDao, SqliteCalendarEventDao};
 pub use daily_summary_dao::{DailySummaryDao, InsertDailySummary, SqliteDailySummaryDao};
 pub use insights_dao::{InsightDao, SqliteInsightDao};
 pub use knowledge_dao::{
-    ConsolidationGroup, EntityFilter, EntityPatch, EntitySort, FactFilter, FactPatch, KnowledgeDao,
-    PersonaFilter, RecentActivity, SqliteKnowledgeDao,
+    ConsolidationGroup, EntityFilter, EntityGraph, EntityPatch, EntitySort, FactFilter, FactPatch,
+    KnowledgeDao, PersonaFilter, RecentActivity, SqliteKnowledgeDao,
 };
 pub use location_dao::{LocationHistoryDao, SqliteLocationHistoryDao};
 pub use persona_dao::{ImportPersona, PersonaDao, PersonaPatch, SqlitePersonaDao};