Upgrade Fedify packages to 2.0.0-dev.396

Pin Fedify dependencies in package.json to 2.0.0-dev.396 and
refresh pnpm-lock.yaml to resolve the same version set.

Update the shared inbox key dispatcher to return a sender identity
object ({ username }) instead of an account owner record, matching
the Fedify 2.0.0-dev.396 dispatcher type contract.

Co-Authored-By: Codex <codex@openai.com>

Author: dahlia

package.json

@@ -21,12 +21,12 @@
   },
   "dependencies": {
     "@aws-sdk/credential-providers": "^3.990.0",
-    "@fedify/fedify": "~2.0.0-dev.387",
-    "@fedify/hono": "~2.0.0-dev.387",
+    "@fedify/fedify": "2.0.0-dev.396",
+    "@fedify/hono": "2.0.0-dev.396",
     "@fedify/markdown-it-hashtag": "~0.3.0",
     "@fedify/markdown-it-mention": "~0.3.0",
-    "@fedify/postgres": "~2.0.0-dev.387",
-    "@fedify/vocab": "~2.0.0-dev.387",
+    "@fedify/postgres": "2.0.0-dev.396",
+    "@fedify/vocab": "2.0.0-dev.396",
     "@hexagon/base64": "^2.0.4",
     "@hono/node-server": "^1.19.9",
     "@hono/zod-validator": "^0.7.6",