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/db/queries.rs

@@ -85,6 +85,57 @@ pub fn delete_project(conn: &Connection, id: &str) -> Result<(), DatabaseError>
     Ok(())
 }
 
+// ── Media Files ──────────────────────────────────────────────────
+
+pub fn create_media_file(
+    conn: &Connection,
+    project_id: &str,
+    file_path: &str,
+) -> Result<MediaFile, DatabaseError> {
+    let id = Uuid::new_v4().to_string();
+    let now = Utc::now().to_rfc3339();
+    conn.execute(
+        "INSERT INTO media_files (id, project_id, file_path, created_at) VALUES (?1, ?2, ?3, ?4)",
+        params![id, project_id, file_path, now],
+    )?;
+    Ok(MediaFile {
+        id,
+        project_id: project_id.to_string(),
+        file_path: file_path.to_string(),
+        file_hash: None,
+        duration_ms: None,
+        sample_rate: None,
+        channels: None,
+        format: None,
+        file_size: None,
+        created_at: now,
+    })
+}
+
+pub fn get_media_files_for_project(
+    conn: &Connection,
+    project_id: &str,
+) -> Result<Vec<MediaFile>, DatabaseError> {
+    let mut stmt = conn.prepare(
+        "SELECT id, project_id, file_path, file_hash, duration_ms, sample_rate, channels, format, file_size, created_at FROM media_files WHERE project_id = ?1 ORDER BY created_at",
+    )?;
+    let rows = stmt.query_map(params![project_id], |row| {
+        Ok(MediaFile {
+            id: row.get(0)?,
+            project_id: row.get(1)?,
+            file_path: row.get(2)?,
+            file_hash: row.get(3)?,
+            duration_ms: row.get(4)?,
+            sample_rate: row.get(5)?,
+            channels: row.get(6)?,
+            format: row.get(7)?,
+            file_size: row.get(8)?,
+            created_at: row.get(9)?,
+        })
+    })?;
+    Ok(rows.collect::<Result<Vec<_>, _>>()?)
+}
+
 // ── Speakers ──────────────────────────────────────────────────────
 
 pub fn create_speaker(
@@ -194,6 +245,39 @@ pub fn reassign_speaker(
     Ok(())
 }
 
+// ── Segments (create) ────────────────────────────────────────────
+
+pub fn create_segment(
+    conn: &Connection,
+    project_id: &str,
+    media_file_id: &str,
+    speaker_id: Option<&str>,
+    start_ms: i64,
+    end_ms: i64,
+    text: &str,
+    segment_index: i32,
+) -> Result<Segment, DatabaseError> {
+    let id = Uuid::new_v4().to_string();
+    conn.execute(
+        "INSERT INTO segments (id, project_id, media_file_id, speaker_id, start_ms, end_ms, text, is_edited, segment_index) VALUES (?1, ?2, ?3, ?4, ?5, ?6, ?7, 0, ?8)",
+        params![id, project_id, media_file_id, speaker_id, start_ms, end_ms, text, segment_index],
+    )?;
+    Ok(Segment {
+        id,
+        project_id: project_id.to_string(),
+        media_file_id: media_file_id.to_string(),
+        speaker_id: speaker_id.map(String::from),
+        start_ms,
+        end_ms,
+        text: text.to_string(),
+        original_text: None,
+        confidence: None,
+        is_edited: false,
+        edited_at: None,
+        segment_index,
+    })
+}
+
 // ── Words ─────────────────────────────────────────────────────────
 
 pub fn get_words_for_segment(
@@ -217,6 +301,31 @@ pub fn get_words_for_segment(
     Ok(rows.collect::<Result<Vec<_>, _>>()?)
 }
 
+pub fn create_word(
+    conn: &Connection,
+    segment_id: &str,
+    word: &str,
+    start_ms: i64,
+    end_ms: i64,
+    confidence: Option<f64>,
+    word_index: i32,
+) -> Result<Word, DatabaseError> {
+    let id = Uuid::new_v4().to_string();
+    conn.execute(
+        "INSERT INTO words (id, segment_id, word, start_ms, end_ms, confidence, word_index) VALUES (?1, ?2, ?3, ?4, ?5, ?6, ?7)",
+        params![id, segment_id, word, start_ms, end_ms, confidence, word_index],
+    )?;
+    Ok(Word {
+        id,
+        segment_id: segment_id.to_string(),
+        word: word.to_string(),
+        start_ms,
+        end_ms,
+        confidence,
+        word_index,
+    })
+}
+
 #[cfg(test)]
 mod tests {
     use super::*;