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/tests/logging_test.rs

@@ -6,22 +6,22 @@ use std::path::Path;
 #[test]
 fn test_log_files_created() {
     // This test verifies that the logging functions work correctly
-    // by checking that files can be created in the logs directory
+    // by checking that files can be created in the discovery directory
 
-    // Clean up any existing test logs
-    let _ = fs::remove_dir_all("logs");
+    // Clean up any existing test discovery dir
+    let _ = fs::remove_dir_all(".g3/discovery");
 
-    // Create logs directory
-    fs::create_dir_all("logs").expect("Failed to create logs directory");
+    // Create discovery directory
+    fs::create_dir_all(".g3/discovery").expect("Failed to create discovery directory");
 
     // Verify directory exists
-    assert!(Path::new("logs").exists());
-    assert!(Path::new("logs").is_dir());
+    assert!(Path::new(".g3/discovery").exists());
+    assert!(Path::new(".g3/discovery").is_dir());
 
     // Test writing a code report
     let test_report = "Test codebase report\nLine 2\nLine 3";
     let timestamp = chrono::Local::now().format("%Y%m%d_%H%M%S").to_string();
-    let report_filename = format!("logs/code_report_{}.log", timestamp);
+    let report_filename = format!(".g3/discovery/code_report_{}.log", timestamp);
 
     fs::write(&report_filename, test_report).expect("Failed to write code report");
     assert!(Path::new(&report_filename).exists());
@@ -30,7 +30,7 @@ fn test_log_files_created() {
     assert_eq!(content, test_report);
 
     // Test writing discovery commands
-    let commands_filename = format!("logs/discovery_commands_{}.log", timestamp);
+    let commands_filename = format!(".g3/discovery/discovery_commands_{}.log", timestamp);
     let test_commands =
         "# Discovery Commands\n# Generated by g3-planner\n\nls -la\ncat README.md\n";