docs: fix stale PLATFORM_URL defaults — platform:8080 → host.docker.internal:8080

Fixes the outdated `http://platform:8080` default hostname in three
files. All workspace runtime modules now default to
`http://host.docker.internal:8080` (molecule-ai-workspace-runtime #12);
docs must match.

Files changed:
- agent-runtime/workspace-runtime.md: example env block default
- architecture/molecule-technical-doc.md: Workspace Runtime env table
- development/local-development.md: .env.example comment

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

content/docs/agent-runtime/workspace-runtime.md

@@ -42,7 +42,7 @@ Common runtime environment variables:
 ```bash
 WORKSPACE_ID=ws-123
 WORKSPACE_CONFIG_PATH=/configs
-PLATFORM_URL=http://platform:8080
+PLATFORM_URL=http://host.docker.internal:8080
 PARENT_ID=
 AWARENESS_URL=http://awareness:37800
 AWARENESS_NAMESPACE=workspace:ws-123

content/docs/architecture/molecule-technical-doc.md

@@ -929,7 +929,7 @@ Postgres + Redis + Langfuse only (for local development without containerized wo
 |----------|---------|---------|
 | `WORKSPACE_ID` | `workspace-default` | Unique workspace identifier |
 | `WORKSPACE_CONFIG_PATH` | `/configs` | Config directory mount |
-| `PLATFORM_URL` | `http://platform:8080` | Platform connection |
+| `PLATFORM_URL` | `http://host.docker.internal:8080` | Platform connection |
 | `PARENT_ID` | Empty | Parent workspace ID (set if nested) |
 | `AWARENESS_URL` | Optional | Awareness service |
 | `AWARENESS_NAMESPACE` | Optional | Scoped namespace for awareness memory |

content/docs/development/local-development.md

@@ -66,7 +66,7 @@ WORKSPACE_ID=           # assigned by platform on provision
 WORKSPACE_CONFIG_PATH=  # path to config folder inside container
 MODEL_PROVIDER=         # e.g. anthropic:claude-sonnet-4-6
 TIER=                   # 1, 2, 3, or 4
-PLATFORM_URL=           # http://platform:8080
+PLATFORM_URL=           # http://host.docker.internal:8080 (in Docker) or http://localhost:8080 (on host)
 PARENT_ID=              # set by platform during team expansion (empty for top-level)
 ANTHROPIC_API_KEY=      # or OPENAI_API_KEY, etc.
 LANGFUSE_HOST=          # http://langfuse-web:3000 (internal container port; host-mapped to :3001)