docs(P21): restructure docs/ into Jekyll Pages site (REQ-54, REQ-55, REQ-56)

---ci---
project: acdl
phase: 21
milestone: v1.6
status: execute
---/ci---

Restructure docs/ into a Jekyll-style GitHub Pages site:
- docs/_config.yml (Pages config + nav, excludes internal/)
- docs/index.md (landing: platform + consumer model, Features, Roadmap)
- docs/modules/index.md (catalog: primitives + modules, normalized terms)
- docs/contracts/index.md (schema, fields, sample, multi-contract)
- docs/pipeline/index.md (CI + deploy pipeline, stages mermaid, streaming)
- docs/pipeline/versioning.md (module + deploy-pipeline versioning)
- docs/environments/index.md (platform-managed envs + onboarding, REQ-61)
- docs/consumer-guide.md (renamed from CONSUMER_GUIDE.md; GitHub-only,
  no .gitea, forge->platform runners, L2->modules, composition->pattern,
  updated mermaid with security-checks + infrastructure-apply)
- docs/architecture.md (consolidated from architecture.md +
  architecture-v1.0.md, current-architecture only, normalized terms:
  primitives/modules, platform runners, no L1/L2/forge/gitea in prose)
- Removed docs/architecture-v1.0.md (consolidated) + docs/CONSUMER_GUIDE.md
  (renamed).

No .ciagent/ or .gitea/ references in docs/. Consumer-facing terminology
normalized (L2->modules, L1->primitives, composition->pattern, forge->
platform runners).

docs/_config.yml

@@ -0,0 +1,33 @@
+title: ACDL — Agentic Cloud Delivery Platform
+description: Consumer + platform-engineer documentation for the ACDL platform.
+theme: jekyll-rtd-theme
+remote_theme: mmistakes/minimal-mistakes@9.0.4
+
+exclude:
+  - internal/
+
+defaults:
+  - scope:
+      path: ""
+    values:
+      layout: single
+
+nav:
+  - title: Overview
+    url: /
+  - title: Consumer Guide
+    url: /consumer-guide/
+  - title: Modules
+    url: /modules/
+  - title: Contracts
+    url: /contracts/
+  - title: Pipeline
+    url: /pipeline/
+  - title: Versioning
+    url: /pipeline/versioning/
+  - title: Environments
+    url: /environments/
+  - title: Architecture
+    url: /architecture/
+  - title: Vision
+    url: /vision/