feat: add Phase 4 Logging & Tracking — inline set logging, history views

Add workout logging so users can track sets, reps, weight, and a
"felt easy?" toggle inline from the workout day view via HTMX.
Sessions auto-create on first log. History page shows past sessions
with detailed per-exercise breakdowns.

New services: WorkoutSessionService, LogService
New routes: POST /log, /log/{id}/edit, /log/{id}/delete, GET /history, /history/{id}
New templates: log_form, log_entry, session_card, log_history, session_detail
Modified: exercise_card (inline logging), nav (History link), workouts route (session context)

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

app/templates/partials/log_entry.html

@@ -0,0 +1,39 @@
+<!-- Displays logged sets for a single exercise within a session -->
+{% if logs %}
+<table>
+    <thead>
+        <tr>
+            <th>Set</th>
+            <th>Reps</th>
+            <th>Weight</th>
+            <th>Easy?</th>
+            <th>Actions</th>
+        </tr>
+    </thead>
+    <tbody>
+        {% for log in logs %}
+        <tr>
+            <td>{{ log.set_number }}</td>
+            <td>{{ log.reps_completed }}</td>
+            <td>{{ log.weight_used }}</td>
+            <td>{{ "Yes" if log.felt_easy else "No" }}</td>
+            <td>
+                <form hx-post="/log/{{ log.id }}/delete"
+                      hx-target="#logs-exercise-{{ exercise_id }}"
+                      hx-swap="innerHTML"
+                      hx-confirm="Delete this set?"
+                      style="display:inline; margin:0;">
+                    <button type="submit" class="outline secondary"
+                            style="padding:0.2rem 0.5rem; font-size:0.8rem;">
+                        Delete
+                    </button>
+                </form>
+            </td>
+        </tr>
+        {% endfor %}
+    </tbody>
+</table>
+{% endif %}
+
+<!-- Next set form -->
+{% include "partials/log_form.html" %}