[1.11] Add prompt injection protection hooks

[vbonk]

What needs to be done

Create .claude/hooks/ directory with template hooks for input validation:

• validate-pr-body.sh.template — Scans PR descriptions for injection patterns
• warn-ai-config-changes.sh.template — Warns when AI config files modified

Templates (not active hooks) — users copy to activate.

Acceptance Criteria

• .claude/hooks/ directory exists with 2 template files
• Each has documentation comments explaining prompt injection
• init-template offers to activate

[vbonk]

Completed in Phase 1 PR #87.