Fix confusing documentation references

1. architecture.md: Fixed diagram to show 'studio' instead of 'g3-console'
   (the crate was renamed during development)

2. analysis/memory.md: Removed reference to non-existent machine_ui_writer.rs

3. theme.rs: Clarified that 'retro' is a theme option (the default theme),
   not a separate TUI mode. No --retro CLI flag exists.

docs/architecture.md

@@ -49,8 +49,7 @@ G3 follows a **tool-first philosophy**: instead of just providing advice, it act
          ┌───────────────────────┼───────────────────────┐
          │                       │                       │
 ┌─────────────────┐    ┌─────────────────┐
-│ g3-ensembles    │    │   g3-console    │
-│                 │    │   studio        │
+│ g3-ensembles    │    │     studio      │
 │ • Flock mode    │    │                 │
 │ • Multi-agent   │    │ • Worktree mgmt │
 │ • Parallel dev  │    │ • Session mgmt  │