release(v4.8.3): cross-channel msgId dedup + Shade.aliasSession

Two follow-ups to the V4.8.2 duplicate-fan-out fixes Prism filed.

1. `Inbox.acceptBridgeFrame(blob)` + shared 4096-entry msgId LRU.
   The relay durably stores blobs and pushes them to every active
   delivery channel; without a cross-channel ack the bridge frame
   ran first and the next inbox-poll re-dispatched the same blob
   ~30 s later, tripping on consumed prekeys. Bridge consumers now
   plumb pushed frames through `acceptBridgeFrame`, which shares
   the dedup gate + ack path with `pollOnce`. Whichever channel
   delivers first wins; the other acks-and-skips. Inbox records
   the msgId before the ack so a parallel poll can't observe an
   in-flight ack window.

2. `Shade.aliasSession(oldLabel, newLabel)`. First-contact forces
   the receiver to label the new session by the relay's sender
   fingerprint hint (`fp:<senderfp>`); the post-decrypt plaintext
   typically announces the peer's real address. Aliasing moves
   session, trusted identity, peer-verification, and identity-
   version under the canonical label. Holds the per-peer mutex on
   both labels (lexicographic order) so concurrent crypto ops can't
   observe a half-moved state. Refuses to overwrite an existing
   session at the new label.

Wire change: `IncomingMessage.expiresAt?` now surfaces the relay's
expiry so receivers can pass bridge frames straight to
`acceptBridgeFrame` without inventing a TTL.

Tests cover bridge-then-poll, poll-then-bridge, aliasSession happy
path, refuse-to-overwrite, and same-label no-op.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

packages/shade-key-transparency/package.json

@@ -1,6 +1,6 @@
 {
   "name": "@shade/key-transparency",
-  "version": "4.8.2",
+  "version": "4.8.3",
   "type": "module",
   "main": "src/index.ts",
   "types": "src/index.ts",