Add project save/load and improve AI chat formatting

Project persistence:
- save_project_transcript command: persists segments, speakers, words to SQLite
- load_project_transcript command: loads full transcript with nested words
- delete_project command: soft-delete projects
- Auto-save after pipeline completes (named from filename)
- Project dropdown in header to switch between saved transcripts
- Projects load audio, segments, and speakers from database

AI chat improvements:
- Markdown rendering in assistant messages (headers, lists, bold, italic, code)
- Better message spacing and visual distinction (border-left accents)
- Styled markdown elements matching dark theme
- Improved empty state and quick action button sizing

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

src-tauri/src/lib.rs

@@ -9,7 +9,10 @@ use tauri::Manager;
 
 use commands::ai::{ai_chat, ai_configure, ai_list_providers};
 use commands::export::export_transcript;
-use commands::project::{create_project, get_project, list_projects};
+use commands::project::{
+    create_project, delete_project, get_project, list_projects, load_project_transcript,
+    save_project_transcript,
+};
 use commands::settings::{load_settings, save_settings};
 use commands::system::{get_data_dir, llama_list_models, llama_start, llama_status, llama_stop};
 use commands::transcribe::{download_diarize_model, run_pipeline, transcribe_file};
@@ -34,6 +37,9 @@ pub fn run() {
             create_project,
             get_project,
             list_projects,
+            delete_project,
+            save_project_transcript,
+            load_project_transcript,
             transcribe_file,
             run_pipeline,
             download_diarize_model,