fix(cli): accept the app's effort key in MessageMetaSchema

[chphch]

The effort picker never reaches the SDK

happy-app sends the per-message effort under meta.effort (sync.ts:728). The CLI parses incoming messages with UserMessageSchema.safeParse (apiSession.ts:552), and MessageMetaSchema does not declare effort — so Zod, which strips unknown keys by default, removes it before anything downstream sees it.

runClaude then gates on the key that is already gone:

if (message.meta?.hasOwnProperty('effort')) {          // always false
    const incoming = (message.meta as Record<string, unknown>).effort;

The cast is the tell. effort is read through Record<string, unknown> precisely because it is absent from MessageMeta, so typecheck passes while the branch that applies the picked effort is unreachable. Every user message falls through to the else and keeps whatever effort the session was spawned with.

Reproduction

Parsing a message shaped exactly like the one the app sends, against this file before and after the change:

	meta after parse	meta?.hasOwnProperty('effort')
main	{"sentFrom":"app"}	false
this branch	{"sentFrom":"app","effort":"high"}	true

Input in both cases: {"sentFrom":"app","effort":"high"}.

Why the tests don't catch it

runClaude.test.ts builds meta as a TypeScript object literal and hands it straight to the loop, so it never crosses the schema. The mismatch exists only on the wire path, which no test exercises.

The change

One field on MessageMetaSchema. Nullable and optional to match the reset semantics the surrounding fields use, and the same null = reset behaviour runClaude already implements.

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_{CI on this PR fails at the install step for the reason in #1663 (pnpm-lock.yaml out of sync with happy-cli/package.json since e7e0ff6), not because of this change.}