fix(contracts): specify the bundled <C4/...> stdlib include for C4 diagrams

Closes #500.

The architecture-documentation contract said building blocks use C4
"with the C4-PlantUML standard library (local include …)". "Local
include" was ambiguous: a recovery run read it as "vendor the
C4-PlantUML files into the repo" and emitted !include c4/C4_Container.puml
pointing at copies it never committed — unresolvable includes.

There are three include forms; only one is intended:
- !include https://...      — remote fetch, Kroki cannot resolve it
- !include c4/C4_Container.puml — vendored copies in the repo
- !include <C4/C4_Container> — PlantUML's bundled stdlib, no repo
  files, no network — this is the one

Contract now names the `!include <C4/...>` stdlib form (angle brackets)
explicitly and rules out both the remote URL and vendored copies.
template + templateDe updated; llms.txt regenerated.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

Author: raifdmueller

website/public/data/contracts.json

@@ -28,8 +28,8 @@
     "description": "How we document architecture with diagrams, ADRs, and decision evaluation",
     "descriptionDe": "Wie wir Architektur mit Diagrammen, ADRs und Entscheidungsbewertung dokumentieren",
     "anchors": ["arc42", "c4-diagrams", "adr-according-to-nygard", "pugh-matrix"],
-    "template": "Architecture documentation follows arc42.\n\nEvery context, building-block and runtime chapter carries at least one diagram. Diagrams are PlantUML, not Mermaid; building blocks use C4 with the C4-PlantUML standard library (local include, not the remote URL — Kroki cannot fetch it), not generic boxes.\n\nDecisions are ADRs (Nygard) with a 3-point Pugh Matrix (-1/0/+1). When the rationale is unconfirmed, ADR Status is \"Accepted (inferred)\" and Pugh cells needing team judgment are marked `?` rather than guessed.",
-    "templateDe": "Architekturdokumentation folgt arc42.\n\nJedes Kontext-, Baustein- und Laufzeit-Kapitel enthält mindestens ein Diagramm. Diagramme sind PlantUML, nicht Mermaid; Bausteine als C4 mit der C4-PlantUML Standard Library (lokales Include, nicht die Remote-URL — Kroki kann sie nicht laden), nicht als generische Kästen.\n\nEntscheidungen sind ADRs (Nygard) mit einer 3-Punkt-Pugh-Matrix (-1/0/+1). Wenn die Begründung unbestätigt ist, lautet der ADR-Status \"Accepted (inferred)\", und Pugh-Zellen, die Team-Urteil erfordern, werden mit `?` markiert statt geraten.",
+    "template": "Architecture documentation follows arc42.\n\nEvery context, building-block and runtime chapter carries at least one diagram. Diagrams are PlantUML, not Mermaid; building blocks use C4 via PlantUML's bundled C4-PlantUML standard library — the `!include <C4/...>` stdlib form (angle brackets), never the remote `https://` URL and never vendored file copies. Not generic boxes.\n\nDecisions are ADRs (Nygard) with a 3-point Pugh Matrix (-1/0/+1). When the rationale is unconfirmed, ADR Status is \"Accepted (inferred)\" and Pugh cells needing team judgment are marked `?` rather than guessed.",
+    "templateDe": "Architekturdokumentation folgt arc42.\n\nJedes Kontext-, Baustein- und Laufzeit-Kapitel enthält mindestens ein Diagramm. Diagramme sind PlantUML, nicht Mermaid; Bausteine als C4 über PlantUMLs gebündelte C4-PlantUML Standard Library — die `!include <C4/...>`-stdlib-Form (spitze Klammern), nie die Remote-`https://`-URL und nie ins Repo kopierte Dateien. Keine generischen Kästen.\n\nEntscheidungen sind ADRs (Nygard) mit einer 3-Punkt-Pugh-Matrix (-1/0/+1). Wenn die Begründung unbestätigt ist, lautet der ADR-Status \"Accepted (inferred)\", und Pugh-Zellen, die Team-Urteil erfordern, werden mit `?` markiert statt geraten.",
     "category": "architecture"
   },
   {

website/public/llms.txt

@@ -6263,7 +6263,7 @@ Document the result as a PRD (problem, goals, personas, success criteria, scope)
 
 Architecture documentation follows arc42.
 
-Every context, building-block and runtime chapter carries at least one diagram. Diagrams are PlantUML, not Mermaid; building blocks use C4 with the C4-PlantUML standard library (local include, not the remote URL — Kroki cannot fetch it), not generic boxes.
+Every context, building-block and runtime chapter carries at least one diagram. Diagrams are PlantUML, not Mermaid; building blocks use C4 via PlantUML's bundled C4-PlantUML standard library — the `!include <C4/...>` stdlib form (angle brackets), never the remote `https://` URL and never vendored file copies. Not generic boxes.
 
 Decisions are ADRs (Nygard) with a 3-point Pugh Matrix (-1/0/+1). When the rationale is unconfirmed, ADR Status is "Accepted (inferred)" and Pugh cells needing team judgment are marked `?` rather than guessed.