Remove legacy logs/ directory, consolidate all data under .g3/

This change removes the legacy logs/ directory and consolidates all
session data, error logs, and discovery files under the .g3/ directory.

New directory structure:
- .g3/sessions/<session_id>/session.json - session logs
- .g3/errors/ - error logs (was logs/errors/)
- .g3/background_processes/ - background process logs
- .g3/discovery/ - planner discovery files (was workspace/logs/)

Changes:
- paths.rs: Remove get_logs_dir()/logs_dir(), add get_errors_dir(),
  get_background_processes_dir(), get_discovery_dir()
- session.rs: Anonymous sessions now use .g3/sessions/anonymous_<ts>/
- error_handling.rs: Errors now saved to .g3/errors/
- project.rs: Remove logs_dir() and ensure_logs_dir() methods
- feedback_extraction.rs: Remove logs_dir field and fallback logic
- planner: Use .g3/ for workspace data and .g3/discovery/ for reports
- flock.rs: Look for session metrics in .g3/sessions/
- coach_feedback.rs: Remove fallback to logs/ path
- Update all tests to use new paths
- Update README.md and .gitignore

crates/g3-planner/src/llm.rs

@@ -324,15 +324,13 @@ pub async fn call_refinement_llm_with_tools(
     let ui_writer = PlannerUiWriter::new();
     
     // CRITICAL FIX: Use the actual workspace directory, NOT codepath!
-    // The workspace is where logs should be written (e.g., /tmp/g3_test_workspace)
+    // The workspace is where session data should be written (e.g., /tmp/g3_test_workspace)
     // The codepath is where the source code lives (e.g., ~/RustroverProjects/g3)
-    // Previous bug: was using codepath as workspace, causing logs to go to wrong location
     let workspace_path = std::path::PathBuf::from(workspace);
     let project = Project::new(workspace_path.clone());
     project.ensure_workspace_exists()?;
     project.enter_workspace()?;
-    
-    project.ensure_logs_dir()?;
+
     // Create agent - not autonomous mode, just regular agent with tools
     let mut agent = Agent::new_with_readme_and_quiet(
         planner_config,