fix(provider): make Claude SDK opt-in

[onmax]

@t3tools/provider-runtime currently installs and evaluates the Claude Agent SDK for every embedded consumer. That also lets the SDK install a platform binary of roughly 324 MB, even when the consumer uses Codex only.

This change loads the SDK only when Claude starts and keeps it as a development-only dependency of the embedded package. Consumers install it explicitly when they select Claude. Cancellation during the deferred import closes a late runtime without starting a query. An optional peer is deliberately avoided because pnpm auto-installs it.

Before / after

Before	After
Importing the provider runtime evaluates the Claude SDK.	Importing the provider runtime does not resolve the SDK.
Codex-only consumers install the Claude SDK and its optional native package.	A packed consumer installs and imports without the Claude SDK present.
Interrupting startup can race a delayed import.	An interrupted import cannot start a Claude query.

The corresponding source change is also proposed upstream in pingdotgg/t3code#8104. This fork PR adds the package contract needed by the separately published @t3tools/provider-runtime package.

Verification

• focused Claude adapter and provider tests: 75 passed
• provider-runtime tests: 1 passed
• provider-runtime build passed
• packed consumer installed and imported without @anthropic-ai/claude-agent-sdk
• packed output retains a deferred SDK import

The provider-runtime typecheck still reports the existing contracts mismatch around mcp_elicitation_approval; this branch does not change that contract.

Created with the Codex harness using gpt-5.6-sol.

[pkg-pr-new]

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commit: ace4e6c