fix: silence hooks when Node is unavailable

[ousamabenyounes]

Route Claude and Codex lifecycle hooks through a cross-platform launcher that exits quietly when Node is unavailable while preserving normal hook behavior.

Test verification (RED → GREEN)

With the fix reverted, the new test fails (RED):

TAP version 13
# Subtest: shared hooks exit quietly when node is unavailable (\#708)
not ok 1 - shared hooks exit quietly when node is unavailable (\#708)
  ---
  duration_ms: 6.557026
  type: 'test'
  location: '/home/ousama/www/public/ousamabenyounes/ponytail/tests/hooks-windows.test.js:57:1'
  failureType: 'testCodeFailure'
  error: |-
    hook failed without node: /bin/sh: 1: node: not found
    
    
    127 !== 0
    
  code: 'ERR_ASSERTION'
  name: 'AssertionError'
  expected: 0
  actual: 127
  operator: 'strictEqual'
  stack: |-
    TestContext.<anonymous> (/home/ousama/www/public/ousamabenyounes/ponytail/tests/hooks-windows.test.js:64:12)
    Test.runInAsyncScope (node:async_hooks:214:14)
    Test.run (node:internal/test_runner/test:1047:25)
    Test.start (node:internal/test_runner/test:944:17)
    startSubtestAfterBootstrap (node:internal/test_runner/harness:296:17)
  ...
1..1
# tests 1
# suites 0
# pass 0
# fail 1
# cancelled 0
# skipped 0
# todo 0
# duration_ms 96.191256

With the fix applied, the test passes (GREEN):

TAP version 13
# Subtest: shared hooks exit quietly when node is unavailable (\#708)
ok 1 - shared hooks exit quietly when node is unavailable (\#708)
  ---
  duration_ms: 16.748734
  type: 'test'
  ...
1..1
# tests 1
# suites 0
# pass 1
# fail 0
# cancelled 0
# skipped 0
# todo 0
# duration_ms 115.226943

Full local suite

Command: node scripts/check-rule-copies.js && node scripts/check-versions.js && npm test

# tests 23
# suites 0
# pass 23
# fail 0
# cancelled 0
# skipped 0
# todo 0
# duration_ms 130.213113

> ponytail-mcp@4.9.0 test
> node --test ./test/*.test.js

TAP version 13
# Subtest: resolveMode keeps valid intensities
ok 1 - resolveMode keeps valid intensities
  ---
  duration_ms: 2.766971
  type: 'test'
  ...
# Subtest: resolveMode falls back to a runtime intensity for off/unknown/empty
ok 2 - resolveMode falls back to a runtime intensity for off/unknown/empty
  ---
  duration_ms: 1.007104
  type: 'test'
  ...
# Subtest: buildInstructions returns the ruleset tagged with the resolved mode
ok 3 - buildInstructions returns the ruleset tagged with the resolved mode
  ---
  duration_ms: 0.933625
  type: 'test'
  ...
1..3
# tests 3
# suites 0
# pass 3
# fail 0
# cancelled 0
# skipped 0
# todo 0
# duration_ms 89.781739

Fix #708