fix: resolve all shellcheck warnings and security issues

- fix(shellcheck): SC2016 in encryption-setup.sh - remove non-expanding $(blkid...)
- fix(shellcheck): SC1091 in firewall-setup.sh and security-hardening.sh - add disable directives
- security: SSH PasswordAuthentication yes -> no (PRD FR-006 violation)
- fix: date expansion in encryption-validation.sh heredoc
- docs: create SDLC.md with TDD workflow and security requirements
- docs: update AGENTS.md to reference SDLC.md
- chore: update STATUS.md with build completion
- chore: minor build-iso.sh output formatting

All 78 tests pass (63 run, 15 skip for libvirt).
Zero shellcheck warnings.

💘 Generated with Crush

Assisted-by: GLM-5 via Crush <crush@charm.land>

AGENTS.md

@@ -143,6 +143,7 @@
 ├── JOURNAL.md             # AI memory - ADRs, patterns, lessons learned
 ├── PRD.md                 # Product requirements
 ├── AGENTS.md              # Agent guidelines (START HERE)
+├── SDLC.md                # Software Development Lifecycle (READ THIS)
 └── docs/                  # Detailed documentation
     ├── TEST-COVERAGE.md   # Test suite coverage
     ├── VERIFICATION-REPORT.md  # Compliance verification
@@ -243,6 +244,7 @@ git log --oneline -10
 #### 2. UNDERSTAND REQUIREMENTS
 - Read MANDATORY SECURITY REQUIREMENTS (above)
 - Review PRD.md for detailed requirements
+- Read SDLC.md for development workflow (CRITICAL)
 - Check AGENTS.md for critical constraints
 - Understand Docker-only workflow