feat(cli): shorten file paths in tool output display

Add three-level path shortening hierarchy for cleaner CLI output:
1. Project path -> <project_name>/... (when project loaded via /project)
2. Workspace path -> ./... (relative to current working directory)
3. Home path -> ~/... (fallback for paths under home directory)

Changes:
- Add shorten_path() and shorten_paths_in_command() functions in display.rs
- Add project_path/project_name fields to ConsoleUiWriter
- Add set_workspace_path(), set_project_path(), clear_project() to UiWriter trait
- Add ui_writer() getter to Agent struct
- Wire up project path setting in /project and /unproject commands
- Set workspace path when creating agents in all CLI modes

Before: ● read_file | /Users/dhanji/icloud/butler/projects/appa_estate/status.md
After:  ● read_file | appa_estate/status.md (with project loaded)
        ● read_file | ./src/main.rs (workspace-relative)
        ● read_file | ~/Documents/file.txt (home-relative)

crates/g3-cli/src/agent_mode.rs

@@ -175,6 +175,7 @@ pub async fn run_agent_mode(
     let ui_writer = ConsoleUiWriter::new();
     // Set agent mode on UI writer for visual differentiation (light gray tool names)
     ui_writer.set_agent_mode(true);
+    ui_writer.set_workspace_path(workspace_dir.clone());
     let mut agent =
         Agent::new_with_custom_prompt(config, ui_writer, system_prompt, combined_content.clone()).await?;