refactor: sqlc vs raw SQL — hybrid approach (R3)

Deleted 8 genuinely unused sqlc queries (no inline equivalent):
- UpsertCurrentRelationship, ListEntitiesCapped, ListEntityStatus,
  UpdateSignalState, InsertClassification, InsertFeedback, InsertSkill,
  UpsertCurrentRelationship — all had zero call sites.

Migrated 9 inline raw SQL sites to use sqlc queries:
- GetOntology (impl.go): ListEntityTypes, ListRelationshipTypes,
  ListLifecycleDefs — replaces 3 raw pool.Query blocks with typed sqlcgen
  calls, eliminating manual row scanning.
- EndRelationship (phase3.go): EndCurrentRelationship — replaces tx.Exec
  with sqlcgen.New(tx).EndCurrentRelationship.
- checkPrecondition (impl.go): GetEntityStatus — replaces tx.QueryRow +
  manual Scan with sqlcgen.New(tx).GetEntityStatus.
- GetEntityRelations (impl.go): ListEntityRelations — replaces raw pool.Query
  + scanRelationships helper (now deleted).
- GetGraph (impl.go): ListGraphEdges — replaces raw pool.Query +
  scanRelationships.
- resolveEntityID (impl.go): GetEntityBySlug/GetEntityByID — replaces
  raw pool.QueryRow + Scan.
- createApproval (mcp/server.go): InsertApproval — replaces raw pool.Exec
  with sqlcgen.InsertApproval.

Deleted scanRelationships helper (was only used by the two migrated
graph queries above).

Regenerated sqlcgen — also picks up stale model updates (AgentSession,
SessionPlanStep, SessionQuestion, etc. from recent migrations).

Documented the carve-out in .agents/dev/CONTRIBUTING.md §SQL conventions:
sqlc is the default; raw pool.Query/Exec is reserved for LISTEN/NOTIFY,
dynamic WHERE builders, blast_radius(), and COPY.

go vet, build, httpapi/mcp/db tests all pass. -383/+170 lines.

internal/db/queries/entities.sql

@@ -27,9 +27,6 @@ WHERE e.type IN (SELECT name FROM tt)
 ORDER BY e.slug
 LIMIT sqlc.arg('lim');
 
--- name: ListEntitiesCapped :many
-SELECT e.* FROM entities e ORDER BY e.slug LIMIT $1;
-
 -- name: InsertEntity :one
 INSERT INTO entities (id, slug, type, name, state, attributes)
 VALUES ($1, $2, $3, $4, $5, $6)