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/planner.rs

@@ -777,13 +777,13 @@ pub async fn run_planning_mode(
     // Set G3_WORKSPACE_PATH environment variable EARLY for all logging
     std::env::set_var("G3_WORKSPACE_PATH", workspace_dir.display().to_string());
     
-    // Create logs directory and verify it exists
-    let logs_dir = workspace_dir.join("logs");
-    if !logs_dir.exists() {
-        fs::create_dir_all(&logs_dir)
-            .context("Failed to create logs directory")?;
+    // Create .g3 directory and verify it exists
+    let g3_dir = workspace_dir.join(".g3");
+    if !g3_dir.exists() {
+        fs::create_dir_all(&g3_dir)
+            .context("Failed to create .g3 directory")?;
     }
-    print_msg(&format!("📁 Logs directory: {}", logs_dir.display()));
+    print_msg(&format!("📁 G3 directory: {}", g3_dir.display()));
     
     // Create the LLM provider for planning
     print_msg("🔧 Initializing planner provider...");