feat: agent guardrails — inherit PreToolUse hooks in spawned sessions

[kokevidaurre]

Agents spawned by squads run don't inherit the guardrail.sh hook. They have --allowedTools but nothing blocks destructive git or shell commands DURING execution. Design needed: pass --settings with guardrail config to spawned Claude sessions.

[agents-squads]

Implementation spec: In execution-engine.ts around line 695-720 where claudeArgs is built, check if a guardrail settings file exists (e.g. .claude/guardrail.json in project root or a squads-provided default). If found, add --settings to claudeArgs before the -- separator. The guardrail.json should contain PreToolUse hooks blocking destructive commands (rm -rf, git push --force, git reset --hard). Need to: (1) define default guardrail.json schema, (2) look for it in project root .claude/ directory, (3) add --settings flag to claudeArgs. Add tests for hook inheritance in execution-engine.