feat(dbq): generate session queries

Adds Insert/Get/Touch/Delete helpers over the sessions table.

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

internal/db/queries/sessions.sql

@@ -0,0 +1,16 @@
+-- name: InsertSession :one
+INSERT INTO sessions (user_id, token_hash, user_agent)
+VALUES ($1, $2, $3)
+RETURNING *;
+
+-- name: GetSessionByTokenHash :one
+SELECT * FROM sessions WHERE token_hash = $1;
+
+-- name: TouchSessionLastSeen :exec
+UPDATE sessions SET last_seen_at = now() WHERE id = $1;
+
+-- name: DeleteSession :exec
+DELETE FROM sessions WHERE id = $1;
+
+-- name: DeleteSessionByTokenHash :exec
+DELETE FROM sessions WHERE token_hash = $1;