fix: remove private registry URL from public codebase

Use generic public registry examples (ghcr.io, docker.io, registry.example.com)
instead of private URLs.

Author: explicitcontextualunderstanding

Tests/Container-Compose-DynamicTests/ComposeAdvancedTests.swift

@@ -24,11 +24,10 @@ final class ComposeAdvancedTests {
                 Database tests require an OCI container registry accessible via HTTPS.
                 Apple Container does not support HTTP for RFC1918 private IPs.
                 
-                Options:
-                1. Set OCI_REGISTRY_URL to your registry (e.g., registry.example.com or registry.example.com)
-                2. Use a public registry like docker.io
-                
-                Example: OCI_REGISTRY_URL=registry.example.com swift test
+                Examples:
+                - OCI_REGISTRY_URL=registry.example.com swift test
+                - OCI_REGISTRY_URL=ghcr.io swift test
+                - OCI_REGISTRY_URL=docker.io swift test
                 """)
         }
         return registryURL
@@ -491,7 +490,7 @@ final class ComposeAdvancedTests {
 
 // MARK: - Database Container Tests
  // Requires OCI_REGISTRY_URL environment variable (Apple Container doesn't support HTTP for RFC1918 IPs)
- // Example: OCI_REGISTRY_URL=registry.example.com swift test
+ // Example: OCI_REGISTRY_URL=ghcr.io swift test
 
  @Test("Test database container starts without volume mount issues")
  func testDatabaseContainerStarts() async throws {

docs/DYNAMIC_TEST_PATTERNS.md

@@ -226,15 +226,18 @@ Tests that depend on external images (like `pgmicro`) face:
 // ComposeAdvancedTests.swift
 private func requireRegistryURL() throws -> String {
     guard let registryURL = ProcessInfo.processInfo.environment["OCI_REGISTRY_URL"] else {
-        throw Errors.registryNotConfigured("...")
+        throw Errors.registryNotConfigured("""
+            OCI_REGISTRY_URL environment variable is not set.
+            ...
+            """)
     }
     return registryURL
 }
 ```
 
 Run with custom registry:
 ```bash
-OCI_REGISTRY_URL=registry.example.com swift test
+OCI_REGISTRY_URL=ghcr.io swift test
 ```
 
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