fix: correct SayHookAction exact field type to string | string[]

[ghost]

Summary

• Bug: The exact field on SayHookAction was incorrectly typed as Record<string, unknown> | undefined instead of string | string[] | undefined, forcing TypeScript users to cast manually when using the hook-based say API.
• Fix: Changed the type of exact in SayHookAction to string | string[] | undefined, consistent with SayPhoneNumberHookAction which correctly types exact: string.
• Protection: Added SayHookAction.ts to .fernignore to prevent the fix from being overwritten by future Fern code generation until the upstream API definition is corrected.

Root Cause

The types are auto-generated by Fern from the API definition. The Fern generator incorrectly produced Record<string, unknown> for what should be a string | string[] union type. Since the Fern definition source is not in this repository, the fix is applied directly to the generated output and protected via .fernignore.

Linear Issue

PRO-3057

Test Plan

• Added tests/unit/types/SayHookAction.test.ts with 4 test cases covering: string value, string array value, undefined value, and combined prompt+exact usage
• Verified TypeScript type checker rejects string assignment to the old Record<string, unknown> type (confirming the bug)
• Verified TypeScript type checker accepts string and string[] assignments after the fix
• All 456 tests pass (38 test files)
• Build (CJS + ESM) passes cleanly
• No regressions in existing tests

Changes

File	Change
src/api/types/SayHookAction.ts	exact type: Record<string, unknown> -> string | string[]
.fernignore	Added SayHookAction.ts + test file to prevent Fern overwrite
tests/unit/types/SayHookAction.test.ts	New test file for type correctness