refactor: add user output architecture improvements plan

Add comprehensive refactoring plan for src/presentation/user_output.rs
with 10 proposals organized in 3 phases:

- Phase 0 (Quick Wins): Verbosity filtering, test infrastructure, theme support
- Phase 1 (Strategic): Trait-based message system, parameterized tests
- Phase 2 (Polish): Type-safe channels, buffering, builders, output sinks

Key architectural decision: Use trait-based OutputMessage design where each
message type (ProgressMessage, SuccessMessage, etc.) implements its own
formatting, verbosity requirements, and channel routing. This achieves true
Open/Closed Principle - new message types can be added without modifying
existing code.

Alternative considered: Enum-based messages with centralized formatter.
Discarded because pattern matching on enum variants requires modifying
the formatter for each new message type, violating Open/Closed Principle.

Author: josecelano

docs/refactors/active-refactorings.md

@@ -1,5 +1,6 @@
 # Active Refactoring Plans
 
-| Document                                                                          | Status         | Issue | Target                                 | Created     |
-| --------------------------------------------------------------------------------- | -------------- | ----- | -------------------------------------- | ----------- |
-| [Command Code Quality Improvements](./plans/command-code-quality-improvements.md) | 🚧 In Progress | -     | `ProvisionCommand`, `ConfigureCommand` | Oct 7, 2025 |
+| Document                                                                                  | Status         | Issue | Target                                 | Created      |
+| ----------------------------------------------------------------------------------------- | -------------- | ----- | -------------------------------------- | ------------ |
+| [Command Code Quality Improvements](./plans/command-code-quality-improvements.md)         | 🚧 In Progress | -     | `ProvisionCommand`, `ConfigureCommand` | Oct 7, 2025  |
+| [User Output Architecture Improvements](./plans/user-output-architecture-improvements.md) | 📋 Planning    | -     | `src/presentation/user_output.rs`      | Oct 30, 2025 |