feat(v2): Import archive .msgs files + DB-based message history

Migration now imports all archive files (oldest first) in addition to the
live .msgs file, with deduplication. Archives endpoint and message history
now query SQLite by date instead of reading .msgs files.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

app/routes/api.py

@@ -344,14 +344,23 @@ def get_messages():
 
         # v2: Read messages from Database
         db = _get_db()
-        if db and not archive_date:
-            ch = channel_idx if channel_idx is not None else 0
-            db_messages = db.get_channel_messages(
-                channel_idx=ch,
-                limit=limit or 50,
-                offset=offset,
-                days=days,
-            )
+        if db:
+            if archive_date:
+                # Archive view: query by specific date
+                db_messages = db.get_channel_messages_by_date(
+                    date_str=archive_date,
+                    channel_idx=channel_idx,
+                )
+            else:
+                # Live view: query with limit/offset/days
+                ch = channel_idx if channel_idx is not None else 0
+                db_messages = db.get_channel_messages(
+                    channel_idx=ch,
+                    limit=limit or 50,
+                    offset=offset,
+                    days=days,
+                )
+
             # Convert DB rows to frontend-compatible format
             messages = []
             for row in db_messages:
@@ -378,7 +387,7 @@ def get_messages():
                         msg['echo_count'] = len(echoes)
                         msg['echo_paths'] = [e.get('path', '') for e in echoes]
         else:
-            # Fallback to parser for archive reads
+            # Fallback to parser for file-based reads
             messages = parser.read_messages(
                 limit=limit,
                 offset=offset,
@@ -1065,15 +1074,29 @@ def sync_messages():
 @api_bp.route('/archives', methods=['GET'])
 def get_archives():
     """
-    Get list of available message archives.
+    Get list of available message archives (dates with messages).
 
     Returns:
         JSON with list of archives, each with:
-        - date (str): Archive date in YYYY-MM-DD format
-        - message_count (int): Number of messages in archive
-        - file_size (int): Archive file size in bytes
+        - date (str): Date in YYYY-MM-DD format
+        - message_count (int): Number of messages on that date
     """
     try:
+        # v2: Query distinct dates from SQLite
+        db = _get_db()
+        if db:
+            dates = db.get_message_dates()
+            # Exclude today (that's "Live")
+            from datetime import date as date_cls
+            today = date_cls.today().isoformat()
+            archives = [d for d in dates if d['date'] != today]
+            return jsonify({
+                'success': True,
+                'archives': archives,
+                'count': len(archives)
+            }), 200
+
+        # Fallback to file-based archives
         archives = archive_manager.list_archives()
 
         return jsonify({