refactor(client): name the compile face in every client test filename

A test file under packages/client now says which face it covers:
`*.client.spec.{ts,tsx}` and its `*.client.{ts,tsx}` helpers belong to the
Client aggregate, `*.host.spec.ts` to the host aggregate. The carrier's four
node-half specs take the Host suffix.

The two suffixes are mutually exclusive, so each aggregate excludes the
other's and both keep one broad test glob: `exclude` wins over `include`, and
`packages/client/**` no longer has to be excluded wholesale from the host
program with per-file `files` entries carved back out of it. A Host-face spec
that reaches only Host source therefore needs no cross-face project
reference, which the split-project rule rejects.

vitest still discovers every file through `**/*.spec.{ts,tsx}`.

packages/client/connection/tests/connection.client.spec.ts

@@ -10,7 +10,7 @@ import { describe, expect, it, vi } from 'vitest'
 import type { SessionId } from '../src/client/api.ts'
 import type { ConnectionState } from '../src/client/connection.ts'
 import { ConnectionController } from '../src/client/connection.ts'
-import { FakeApiClient, deferred, ok } from './fake-api.ts'
+import { FakeApiClient, deferred, ok } from './fake-api.client.ts'
 
 const SID = 'fk-c1' as SessionId
 const FAST = { backoffBaseMs: 10, backoffFactor: 1, backoffMaxMs: 10, streamOpenTimeoutMs: 500 }