fix: honest remediation batch 3 - fix broken claims and real Argon2id

Previous commits marked findings as ✅ that were actually superficial or
broken. This commit fixes the real problems honestly.

Real fixes:
- Argon2id KDF: Fixed via preseed partman/early_command that patches
  partman-crypto's cryptsetup luksFormat to include --pbkdf argon2id.
  Previous luks-kdf-configure.sh "auto-conversion" was dead code
  (cryptsetup luksConvertKey needs stdin passphrase, nothing provides it).
  Now the hook is an honest verifier, not a fake converter.
- src/security-hardening.sh: Removed sshd_config generation entirely
  (was still generating it despite claiming client-only)
- AIDE init: Removed || true error swallowing, now reports failures
- COMPLIANCE.md: Marked CMMC L3 and FedRAMP as aspirational targets
  with honest explanation of what's missing (3PAO, org controls)
- VERIFICATION-REPORT.md: Added self-review warning about contradictions,
  fixed wrong preseed path (config/preseed.cfg → includes.installer/)
- Removed phantom knel-compliance-check.sh reference from COMPLIANCE.md
- encryption-setup.sh: README now says "Argon2id (via early_command)"
  instead of bare "Argon2id" which was false
- demo.preseed.cfg: Added same Argon2id early_command
- Added .dockerignore (was missing)
- Fixed .gitignore *key* pattern (too broad, matched keyboard.conf etc)

Still remaining (honest assessment):
- C-06: Git history scrub (needs git-filter-repo, destructive)
- H-09: Build cache integrity (design work needed)
- M-11: Docker base digest pinning
- Phase 3: Test suite overhaul (85% grep-based, not behavioral)
- Phase 4: Documentation cleanup (threat model, etc)
- ISO NOT rebuilt since fixes

786 tests pass, 0 shellcheck warnings.

💘 Generated with Crush

Assisted-by: GLM-5.1 via Crush <crush@charm.land>

.dockerignore

@@ -0,0 +1,40 @@
+# Build artifacts
+output/
+tmp/
+tmp2/
+*.iso
+*.sha256
+*.md5
+*.img
+*.log
+
+# Build intermediates
+knel-build/
+knel-iso/
+knel-custom/
+knel-final/
+artifacts/
+.chroot/
+.cache/
+.build/
+
+# Secrets and keys
+*key*
+*.pem
+*.crt
+*.gpg
+secrets/
+config/secureboot-keys/
+
+# IDE and OS
+.vscode/
+.idea/
+.DS_Store
+*.swp
+*.swo
+*~
+
+# Downloaded files
+debian-*.iso
+*.tar.gz
+*.tar.xz