fix: rebind remote permission handlers after session swap

[wang-kaopu]

Closes #1123

Summary

This PR fixes a remote permission approval issue where tapping approve/deny
on iOS could stay stuck in a loading state after a session/client change.

The root cause was that Claude-side permission handling could remain bound
to an outdated session client after session swap, so permission responses no
longer matched the active pending request.

Changes

• make Session.client updatable in the Claude remote flow
• add Session.updateClient() to sync the active API session client
• add PermissionHandler.updateSession() so the permission RPC handler
  can be rebound after session changes
• rebind the Claude permission handler when the session changes
• update Claude remote flow to use the current API session reference for
  session events/state updates
• add a minimal unit test covering permission handler rebinding after
  session swap

Why this fixes the issue

Remote permission approvals depend on a session-scoped permission RPC
channel. After a session/client change, the old handler could still be
registered against the stale client, which meant iOS approval responses
would not resolve the active pending request.

By rebinding the permission handler and updating the active session client
reference, approval responses are routed back to the current session
correctly.

Validation

• built packages/happy-wire
• ran packages/happy-cli typecheck successfully
• added and ran a minimal unit test:
  • src/claude/utils/permissionHandler.test.ts

Notes

In my local repro flow, this also resolved the similar approval-loading
symptom I was seeing with Codex, although this PR is focused on fixing the
Claude-side session swap gap directly.