Add optional battery metadata fields

New nullable columns on Battery: size, chemistry, capacity_mah,
tested_capacity_mah, tested_date, charge_cycles, purchase_date.

Battery detail page shows all populated fields and a full edit form
with select dropdowns for size and chemistry (with Other fallback).
Capacity health % shown in green/orange/red when both nominal and
tested capacity are set. Dashboard gains a Size column.

app.py

@@ -77,14 +77,31 @@ def create_app(config_object="config"):
     # Battery — edit notes
     # ------------------------------------------------------------------ #
 
-    @app.route("/battery/<int:battery_id>/edit-notes", methods=["POST"])
-    def battery_edit_notes(battery_id):
+    @app.route("/battery/<int:battery_id>/edit-details", methods=["POST"])
+    def battery_edit_details(battery_id):
         battery = db.get(Battery, battery_id)
         if battery is None:
             abort(404)
-        battery.notes = request.form.get("notes", "").strip() or None
+        f = request.form
+
+        def _int(key):
+            v = f.get(key, "").strip()
+            try:
+                return int(v) if v else None
+            except ValueError:
+                return None
+
+        battery.notes               = f.get("notes", "").strip() or None
+        battery.size                = f.get("size", "").strip() or None
+        battery.chemistry           = f.get("chemistry", "").strip() or None
+        battery.capacity_mah        = _int("capacity_mah")
+        battery.tested_capacity_mah = _int("tested_capacity_mah")
+        battery.tested_date         = f.get("tested_date", "").strip() or None
+        battery.charge_cycles       = _int("charge_cycles")
+        battery.purchase_date       = f.get("purchase_date", "").strip() or None
+
         db.commit()
-        flash("Notes updated.", "success")
+        flash("Details updated.", "success")
         return redirect(url_for("battery_detail", battery_id=battery_id))
 
     # ------------------------------------------------------------------ #