docs: fix struct names and add deploy module architecture

- Fix incorrect struct names in architecture docs:
  - diff.md: DefaultDiffer → StackDiffer
  - delete.md: AWSDeleter → StackDeleter
- Update diff.md to match actual implementation:
  - Remove references to non-existent changeset.go
  - Fix CloudFormation client field names
  - Update architecture diagrams
- Add comprehensive deploy.md architecture documentation:
  - Complete StackDeployer documentation
  - Two deployment strategies (new vs existing stacks)
  - Integration with diff engine for change preview
  - User confirmation workflows and safety mechanisms
  - Progress monitoring and error handling strategies
  - Testing architecture and performance considerations

All documentation now accurately reflects current implementation
and follows consistent naming patterns across modules.

Author: orien

docs/architecture/delete.md

@@ -106,7 +106,7 @@ classDiagram
         +DeleteStack(ctx, stack) error
     }
     
-    class AWSDeleter {
+    class StackDeleter {
         -awsClient: Client
         +DeleteStack(ctx, stack) error
         -validateStackExists() bool
@@ -116,7 +116,7 @@ classDiagram
         -waitForCompletion() error
     }
     
-    Deleter <|-- AWSDeleter
+    Deleter <|-- StackDeleter
 ```
 
 **Key Responsibilities:**