Add comprehensive E2E smoke tests for install/update/uninstall

Phase 8: Agent config install E2E — creates stub environment with
all 10 agent detection dirs, runs install -y with isolated HOME,
verifies exact JSON structure, TOML content, hook format, skills,
and merge-not-overwrite behavior for every agent config.

Phase 9: Agent config uninstall E2E — verifies complete removal of
all MCP entries, hooks, instructions while preserving user's existing
config keys. Adversarial tests: idempotent double install, uninstall
without prior install, corrupt JSON/TOML handling, double uninstall.

Phase 10: Platform binary security — macOS: codesign verify, strip
signature, SIGKILL on unsigned arm64 (exit 137), re-sign + verify.
Linux/Windows: verify unsigned binary runs without signing.

Phase 11: Process kill — start MCP server, verify running, kill,
verify gone.

Phase 14: Update flow — binary replacement with signing, read-only
binary edge case, platform-specific verification.

Fix cbm_find_cli: add S_IXUSR check for hardcoded path search
(was missing, only checked for PATH-based search).

Author: DeusData