Persist authenticated private-media delivery receipts (#1466)

Adds a durable receiver-side ledger (BLEPrivateMediaReceiptStore) mapping a deterministic private-media message ID — hash-bound to sender, recipient, and entropy-bearing filename — to the stored file before UI delivery and before the Noise-encrypted delivery ACK, so sender retries and relaunches cannot create duplicate bubbles or files. Receipts are unforgeable without the Noise session; capability bit 9 rides the existing announce bitfield (no wire-format change; rolling upgrade safe both directions).

Includes review fixes: corrupt receipt records are quarantined per-record (bytes preserved at <id>.json.corrupt, only that ID fail-closed — previously one bad record silently disabled ALL inbound private media forever); the panic reset now reaches BLEService's own store instance via completePanicReset with a production-wiring test; and both content.delivery.reason.* strings ship with full 30-locale coverage.

docs/PRIVATE-MEDIA-MIGRATION.md

@@ -28,6 +28,13 @@ peer's Noise session before BLE fragmentation.
   `0x21`. A valid bit-8 proof selects Noise `0x20`; a valid no-bit proof or a
   no-proof timeout reaches the explicit legacy-consent path for an unpinned
   peer. No timeout automatically sends raw bytes.
+- `PeerCapabilities.privateMediaReceipts` is bit 9. Its exact-session
+  authenticated proof enables bounded sender-side automatic retry; a public
+  announce never does. It does not replace bit 8: encrypted `0x20` media from
+  bit-8-only prior iOS clients keeps the same deterministic stable ID and
+  delivery ACK. Receivers durably commit that ID before UI delivery or ACK, so
+  a lost proof followed by a later bit-9 retry cannot create a second,
+  random-ID bubble.
 - An unpinned peer with a stable Noise key but without that capability is
   eligible for one signed, directed
   `fileTransfer`, matching the pre-migration wire form used by older iOS and