Support safer custom Claude Code wrappers

[xiaobaifly7]

Summary

• make HAPI_CLAUDE_PATH a safer Claude Code executable/wrapper override
• preflight custom paths for missing files, likely wrapper recursion, and Windows PATH wrapper loops
• support Windows command/script wrappers by choosing shell mode only when needed
• document Claude-compatible wrapper usage and add focused tests

Why

HAPI already supports HAPI_CLAUDE_PATH, but custom wrappers can fail opaquely when the configured path is missing, recursively invokes itself through a PATH shim, or needs Windows shell execution. This keeps the default Claude discovery behavior unchanged while making opt-in wrappers easier to diagnose.

Validation

• ..\\node_modules\\.bin\\vitest.exe run src\\claude\\sdk\\utils.test.ts src\\claude\\sdk\\query.test.ts
• rtk git diff --check
• tsc --noEmit -p cli\\tsconfig.json --pretty false currently fails on upstream type drift unrelated to this PR (capabilities, message-cancelled, and scheduledAt typing errors outside the changed files).