Diagram generator calibrated from 37 Oracle ref architectures + KB health tooling

Diagram generator (oci_diagram_gen.py):
- Icon sizing calibrated: 63px target height, 45px min width (from 37 Oracle
  Architecture Center .drawio files: 12,617 cells, 234x 63x63 service icons)
- Auto-sizing: containers grow from content, never overflow (validated by script)
- DRG placed outside VCN, inside region (Oracle hub-spoke pattern)
- Gateway stacking uses _calc_service_block_h to prevent label overlap
- Edge labels: mxGeometry offset injection (15-20px away from midpoint)
- Tight icon groups: edges connect to visible icon, not invisible wide group
- VCN/subnet dash pattern corrected to "4 2", stroke to #aa643b (Oracle ref)
- jettySize=auto, dual connection merge, container=1;collapsible=0

New tools:
- scripts/validate-diagram.py: checks icon sizes, overlaps, container overflow
- tools/refresh_arch_catalog.py --check-links: HTTP HEAD check on all 123 URLs
- .gitea/workflows/kb-health.yaml: weekly link + freshness check (Mon 8am UTC)
- kb/diagram/oracle-ref-measurements.md: exact measurements from Oracle refs
- kb/CHANGELOG.md: KB change log shown in welcome banner

SKILL.md:
- Pre-flight: python→python3, silent errors, git fetch check for local users
- Changelog banner in welcome flow
- Anti-hallucination guardrails (from earlier commit, carried forward)

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

examples/output-demo-pharma-mx/diagram-spec.yaml

@@ -77,20 +77,14 @@ tenancy:
             - id: "drg"
               label: "DRG"
               type: "drg"
-              w: 90
-              h: 60
             # IGW — whitelist: public subnet requires it
             - id: "igw"
               label: "Internet\nGateway"
               type: "igw"
-              w: 100
-              h: 60
             # SGW — whitelist: ExaCS backup requires it
             - id: "sgw"
               label: "Service\nGateway"
               type: "service_gateway"
-              w: 100
-              h: 60
 
     # ── DR Region: Sao Paulo ──
     - id: "region_gru"