feat(hooks): polyglot hook wrapper for cross-platform compatibility

[dean0x]

Summary

• Adds polyglot run-hook wrapper that works as both Windows batch and Unix bash
• All hook registrations now use run-hook <name> instead of direct .sh paths
• Replaces set -euo pipefail with set -e in all 5 hook scripts for MSYS/MinGW compatibility
• Skips chmod on Windows in installer

Changes

File	Change
scripts/hooks/run-hook	NEW — polyglot wrapper
scripts/hooks/*.sh (5 files)	set -euo pipefail → set -e
src/cli/commands/ambient.ts	Hook command uses run-hook ambient-prompt
src/cli/commands/memory.ts	Hook commands use run-hook prefix
src/cli/utils/installer.ts	Platform-aware chmod (skip on Win32)
tests/ambient.test.ts	Updated marker assertions
tests/memory.test.ts	Updated marker assertions

Backward Compatibility

Existing installs with old-style .sh hook commands continue working because includes() checks match both ambient-prompt.sh and run-hook ambient-prompt. Old hooks remain functional until users --disable && --enable or re-run devflow init.

Test plan

• npm run build passes
• npm test — all 178 tests pass
• run-hook session-start-memory correctly dispatches to .sh script
• Old .sh marker strings still match via includes() backward compat

Closes #80
Part of #78