Add run tagging (DB column + migration + route + UI)

- Added tags VARCHAR(300) column to Run model
- Added startup ALTER TABLE migration in app.py
- New POST /run/<id>/set_tags route saves comma-separated tags
- Tag badges + collapsible edit form in run_details.html header area

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

web/db.py

@@ -35,6 +35,8 @@ class Run(db.Model):
     progress = db.Column(db.Integer, default=0)
     last_heartbeat = db.Column(db.DateTime, nullable=True)
 
+    tags = db.Column(db.String(300), nullable=True)
+
     logs = db.relationship('LogEntry', backref='run', lazy=True, cascade="all, delete-orphan")
 
     def duration(self):