refactor(ai): drop dead status-batch reverse map, consume the budget type

Remove the unused output-key reverse map the batch path never read, and
have the budget table satisfy the AiBudget interface directly so the type
is enforced rather than orphaned.

src/lib/ai/ai-budgets.ts

@@ -19,8 +19,11 @@
 export interface AiBudget {
   /** Sampling temperature. Low for reference surfaces, slightly higher for chat. */
   temperature: number;
-  /** Output-token ceiling. Sized to the surface's documented output contract. */
-  maxTokens: number;
+  /**
+   * Output-token ceiling. Sized to the surface's documented output contract.
+   * Optional for surfaces whose caller pins its own token const (self-context).
+   */
+  maxTokens?: number;
 }
 
 /**
@@ -94,4 +97,4 @@ export const AI_BUDGETS = {
    * questions. Temperature only; the caller pins its own token const.
    */
   selfContext: { temperature: 0.4 },
-} as const satisfies Record<string, { temperature: number; maxTokens?: number }>;
+} as const satisfies Record<string, AiBudget>;

src/lib/ai/prompts/status-batch.ts

@@ -36,15 +36,6 @@ export const STATUS_BATCH_KEY_BY_METRIC: Record<string, string> = {
   general: "general",
 };
 
-/** Reverse of `STATUS_BATCH_KEY_BY_METRIC` — output key → InsightStatus scope. */
-export const STATUS_BATCH_METRIC_BY_KEY: Record<string, string> =
-  Object.fromEntries(
-    Object.entries(STATUS_BATCH_KEY_BY_METRIC).map(([metric, key]) => [
-      key,
-      metric,
-    ]),
-  );
-
 /**
  * Compose the batch system prompt: the shared assessment scaffold plus the
  * `{ perMetric }` output instruction. `presentKeys` are the output keys for