feat: enhance dashboard with PRs, adherence, activity, progression chart, and muscle heatmap

Add 3 new stat cards (Last Workout, Personal Records, Adherence Rate),
recent activity table, progression timeline chart, and muscle group
recency heatmap to the dashboard. Remove Total Volume card.

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

app/templates/partials/stats_card.html

@@ -4,12 +4,6 @@
         {{ stats.total_sessions }}
     </p>
 </article>
-<article>
-    <header><h4>Total Volume</h4></header>
-    <p style="font-size:2rem; font-weight:700;">
-        {{ "{:,}".format(stats.total_volume) }} lbs
-    </p>
-</article>
 <article>
     <header><h4>Total Sets</h4></header>
     <p style="font-size:2rem; font-weight:700;">
@@ -22,3 +16,38 @@
         {{ stats.current_streak }} week{{ "s" if stats.current_streak != 1 }}
     </p>
 </article>
+</div>
+<div class="grid">
+<article>
+    <header><h4>Last Workout</h4></header>
+    <p style="font-size:2rem; font-weight:700;">
+        {% if stats.last_workout_date %}
+        {{ stats.last_workout_date.strftime('%b %d') }}
+        {% else %}
+        Never
+        {% endif %}
+    </p>
+</article>
+<article>
+    <header><h4>Personal Records</h4></header>
+    <p style="font-size:2rem; font-weight:700;">
+        {{ personal_records|length }} PR{{ "s" if personal_records|length != 1 }}
+    </p>
+    {% if personal_records %}
+    <details>
+        <summary>View records</summary>
+        <ul style="font-size:0.85rem; margin-top:0.5rem;">
+            {% for pr in personal_records[:10] %}
+            <li>{{ pr.exercise_name }}: {{ pr.weight_display }}</li>
+            {% endfor %}
+        </ul>
+    </details>
+    {% endif %}
+</article>
+<article>
+    <header><h4>Adherence</h4></header>
+    <p style="font-size:2rem; font-weight:700;">
+        {{ adherence.rate }}%
+    </p>
+    <small>{{ adherence.completed }}/{{ adherence.expected }} sessions ({{ adherence.weeks }}wk)</small>
+</article>