fix(hooks): write hook output synchronously so process.exit cannot drop it

[DietrichGebert]

Fixes #1043.

Every hook calls process.exit() right after writeHookOutput(). On macOS a write to a pipe is asynchronous, so when the pipe cannot take the whole output at once, the rest is still pending when the process exits and is lost. The host then gets truncated or empty JSON and no ruleset.

writeHookOutput() is the one place all hook output goes through. It now writes with fs.writeSync(1, ...), so the output is complete before any exit. All callers already wrap it in try/catch, so a closed reader (EPIPE) still never fails the hook.

Checked on macOS with a pipe that is already full when the hook starts (the reader drains it only later):

	main	this PR
mode tracker (/ponytail lite)	0 bytes	valid JSON, 2951 chars
subagent	0 bytes	valid JSON, 2859 chars

A reader that closed the pipe: all three hooks exit 0 with no stderr. npm test passes (136 + 29).