[LARGEST] Appendix 30: move ~85% of the code to an external examples repo (-3,700 lines) #1903

Problem

30_appendix_code_examples.md is 4,267 lines = 28% of the whole book. It contains 25+ full production code files copied into running text. In print/PDF they cannot be copied and pasted; they age quickly; several are incomplete (classes with raise NotImplementedError).

Plan

Create a new repo aac-examples/ (or architecture-as-code-examples/) and move the following into it:

Move to external repo

Remove entirely

• 05_CODE_2 Jenkinsfile (~295 lines) — duplicates the GitHub Actions version
• 17_CODE_1–3 (~570 lines) — pseudo-pedagogical YAML/Python not used in production
• 30:2443–2466 References/Conventions with emoji-style guide

Keep in the book (shortened)

• 21_CODE_1 multi-cloud landing zone (~60 lines)
• 10_CODE_1 Rego encryption module (shortened to ~80 lines)
• 13_CODE_J OPA test (representative, ~80 lines)
• 06_CODE_5 Structurizr workspace (shortened to ~100 lines)
• Index of external examples with links (~150 lines)

Template for the book's new style

### 05_CODE_3: Terratest for VPC implementation
*Referenced from chapter 5.*

A full Go Terratest implementation verifying VPC tagging, CIDR ranges, 
and data-residency assertions is maintained in the companion repository:

https://github.com/Geonitab/aac-examples/tree/main/testing/terratest

Key patterns demonstrated:
- Subnet CIDR validation with `terraform.OutputList`
- Tag compliance assertions via `awsSchema`
- Region allow-listing for EU data residency

Expected saving

~3,700 lines (87% of appendix 30).

Source

Review of Parts G & H. See CUT_PROPOSAL.md.