knowledge: list sort + persona-scoped fact_count per entity

Two related additions to /knowledge/entities:

- New EntitySort enum (UpdatedDesc default, NameAsc, FactCountDesc)
  surfaced via `?sort=updated|name|count`. NameAsc clusters near-
  duplicate names so dupes stand out at a glance; FactCountDesc
  surfaces heavily-used entities and demotes 0-fact noise to the
  bottom.

- New `list_entities_with_fact_counts` DAO method that returns each
  entity alongside a persona-scoped count of its non-rejected facts
  (subject side). Persona scope follows X-Persona-Id via the
  existing resolve_persona_filter chain — Single filters on
  (user_id, persona_id), All unions across the user's personas.
  Implemented as one raw SQL query with a LEFT JOIN to a fact-count
  subquery and ORDER BY tied to the chosen sort, so count-sort needs
  no second round trip.

The agent's existing list_entities call site is unchanged — it
doesn't need persona-scoped counts and the trait method stays cheap.
EntitySummary grows an Option<i64> fact_count (skip_serializing_if
none) so PATCH responses stay shaped as before.

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::{
-    EntityFilter, EntityPatch, FactFilter, FactPatch, KnowledgeDao, PersonaFilter, RecentActivity,
-    SqliteKnowledgeDao,
+    EntityFilter, EntityPatch, EntitySort, FactFilter, FactPatch, KnowledgeDao, PersonaFilter,
+    RecentActivity, SqliteKnowledgeDao,
 };
 pub use location_dao::{LocationHistoryDao, SqliteLocationHistoryDao};
 pub use persona_dao::{ImportPersona, PersonaDao, PersonaPatch, SqlitePersonaDao};