Add capacity test history and chart to battery detail

- New CapacityTest model (battery_id FK CASCADE, mah, date, notes)
- DB migration: create capacity_test table, migrate existing single-test data
- Two new routes: add and delete capacity test records
- Battery.tested_capacity_mah/tested_date kept in sync with latest test
  so dashboard display requires no changes
- Battery detail: Capacity History card with sortable table, health %
  per reading, and a canvas line chart (shown when >= 2 records)
- Chart uses CSS variables for colors — works in light and dark mode
- Remove tested_capacity_mah/tested_date from Edit Details form
- 3 new acceptance tests (48 total)

app.py

@@ -2,7 +2,7 @@ from flask import Flask, render_template, redirect, url_for, request, flash, abo
 from sqlalchemy import create_engine, func
 from sqlalchemy.orm import scoped_session, sessionmaker
 
-from models import Base, Battery, Device
+from models import Base, Battery, Device, CapacityTest
 
 
 def create_app(config_object="config"):
@@ -105,8 +105,13 @@ def create_app(config_object="config"):
             .filter(Battery.storage_location.isnot(None))
             .distinct().order_by(Battery.storage_location).all()
         ]
+        capacity_tests = (db.query(CapacityTest)
+                          .filter_by(battery_id=battery_id)
+                          .order_by(CapacityTest.tested_date, CapacityTest.id)
+                          .all())
         return render_template("battery_detail.html", battery=battery,
-                               storage_locations=storage_locations)
+                               storage_locations=storage_locations,
+                               capacity_tests=capacity_tests)
 
     # ------------------------------------------------------------------ #
     # Battery — edit notes
@@ -130,8 +135,6 @@ def create_app(config_object="config"):
         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
         battery.storage_location    = f.get("storage_location", "").strip() or None
@@ -140,6 +143,57 @@ def create_app(config_object="config"):
         flash("Details updated.", "success")
         return redirect(url_for("battery_detail", battery_id=battery_id))
 
+    # ------------------------------------------------------------------ #
+    # Battery — capacity test history
+    # ------------------------------------------------------------------ #
+
+    def _sync_latest_test(battery):
+        latest = (db.query(CapacityTest)
+                  .filter_by(battery_id=battery.id)
+                  .order_by(CapacityTest.tested_date.desc(), CapacityTest.id.desc())
+                  .first())
+        battery.tested_capacity_mah = latest.tested_capacity_mah if latest else None
+        battery.tested_date = latest.tested_date if latest else None
+
+    @app.route("/battery/<int:battery_id>/capacity-test/add", methods=["POST"])
+    def battery_capacity_test_add(battery_id):
+        battery = db.get(Battery, battery_id)
+        if battery is None:
+            abort(404)
+        mah_raw  = request.form.get("tested_capacity_mah", "").strip()
+        date_val = request.form.get("tested_date", "").strip()
+        notes    = request.form.get("notes", "").strip() or None
+        if not mah_raw or not date_val:
+            flash("Capacity (mAh) and date are required.", "error")
+            return redirect(url_for("battery_detail", battery_id=battery_id))
+        try:
+            mah = int(mah_raw)
+            if mah <= 0:
+                raise ValueError
+        except ValueError:
+            flash("Capacity must be a positive integer.", "error")
+            return redirect(url_for("battery_detail", battery_id=battery_id))
+        db.add(CapacityTest(battery_id=battery_id, tested_capacity_mah=mah,
+                            tested_date=date_val, notes=notes))
+        db.flush()
+        _sync_latest_test(battery)
+        db.commit()
+        flash("Test record added.", "success")
+        return redirect(url_for("battery_detail", battery_id=battery_id))
+
+    @app.route("/battery/<int:battery_id>/capacity-test/<int:test_id>/delete", methods=["POST"])
+    def battery_capacity_test_delete(battery_id, test_id):
+        battery = db.get(Battery, battery_id)
+        test    = db.get(CapacityTest, test_id)
+        if battery is None or test is None or test.battery_id != battery_id:
+            abort(404)
+        db.delete(test)
+        db.flush()
+        _sync_latest_test(battery)
+        db.commit()
+        flash("Test record deleted.", "success")
+        return redirect(url_for("battery_detail", battery_id=battery_id))
+
     # ------------------------------------------------------------------ #
     # Battery — assign
     # ------------------------------------------------------------------ #