fix(acks): make 999 source_batch_id unique per file + surface PCN

Gainwell's MFT ships every 999 with the same ISA interchange
control number (`000000001`) and one 999 ack covers a whole
batch, not a single claim — so the AK2 set_control_number
(patient_control_number) is the same for the ~96 999s in a
batch. With the old synthetic-id formula (`999-{icn}`), all 385
daily acks collapsed onto a single row the operator couldn't
distinguish.

The new formula is `999-{pcn}-{filename_hash8}` (or
`999-{icn}-{filename_hash8}` for envelope-only 999s without an
AK2). The PCN gives the operator a human-readable handle to the
claim batch; the 8-char hash of the inbound filename guarantees
uniqueness within a batch. Fits in the VARCHAR(32) source_batch_id
column (max 22 chars).

Also surface `patient_control_number` in /api/acks list response
(extracted from raw_json's set_responses[0].set_control_number)
and in the Acks UI as the primary label, with the synthetic id
shown dimmed after a middle dot. The detail endpoint already
exposed raw_json for the full 999 parse tree.

src/types/index.ts

@@ -529,6 +529,14 @@ export interface Ack {
   receivedCount: number;
   ackCode: "A" | "E" | "R" | "P";
   parsedAt: string;
+  /**
+   * AK2 set_control_number from the inbound 999 — the
+   * patient_control_number of the original claim batch this 999
+   * acks. Surfaced in the list endpoint so the operator can
+   * correlate a 999 to a claim batch in the UI without a second
+   * round-trip to the detail endpoint.
+   */
+  patientControlNumber?: string | null;
 }
 
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