feat: add shared git hooks with setup script

Git hooks were only in .git/hooks/ which isn't tracked by git.
Created a shared githooks/ directory so all contributors get
the pre-commit hook that enforces SDLC requirements.

Changes:
- githooks/pre-commit: Pre-commit hook enforcing SDLC (lint, tests, docs)
- scripts/setup-githooks.sh: Script to configure git core.hooksPath
- README.md: Added first-time setup instructions
- AGENTS.md: Updated startup steps and project structure

Users/agents run ./scripts/setup-githooks.sh after cloning to enable hooks.

Reference: docs/SDLC.md

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README.md

@@ -94,6 +94,12 @@ tail -f /tmp/knel-iso-build.log
 ls -lh output/
 ```
 
+### First-Time Setup (After Cloning)
+```bash
+# Configure git hooks (required for SDLC enforcement)
+./scripts/setup-githooks.sh
+```
+
 ### SDLC Workflow (MANDATORY)
 ```bash
 # After ANY changes: