feat: replace wk1/wk4 targets with 6→8→10→12 rep ladder progression

Simplifies the progression model to a universal rep ladder: every exercise
follows 6→8→10→12 reps at current weight, then +5 lbs and reset to 6.
Replaces per-user wk1/wk4 rep and weight targets with a single
starting_weight field.

- Add Alembic migration to drop wk1_reps/wk4_reps/wk1_weight/wk4_weight,
  add starting_weight (migrated from wk1_weight)
- Run Alembic migrations on app startup instead of create_all, with
  auto-detection and stamping for legacy databases
- Include alembic/ and alembic.ini in Docker image
- Rewrite progression_service.get_suggestion() with ladder logic:
  climb, hold, weight_increase, hold_at_top, deload
- Replace wk1/wk4 grid in exercise cards with rep ladder progress bar
- Add color-coded progression badges by type
- Change weight log input from text to number with pre-filled suggestion
- Normalize weight input in routes (0→BW, bare number→N lbs)
- Remove schedule page (route, template, nav link, tests)
- Simplify user_programs.yaml from 4 fields to 1 per exercise
- Update all tests for new schema and progression logic

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

app/templates/partials/exercise_card.html

@@ -7,16 +7,26 @@
     </header>
 
     {% if program %}
-    <div class="grid">
-        <div>
-            <small>Week 1</small>
-            <p>{{ program.wk1_reps }} reps @ {{ program.wk1_weight }}</p>
-        </div>
-        <div>
-            <small>Week 4</small>
-            <p>{{ program.wk4_reps }} reps @ {{ program.wk4_weight }}</p>
+    {% set suggestion = suggestions[exercise.id] if suggestions and exercise.id in suggestions else None %}
+    {% set pos = suggestion.ladder_position if suggestion and suggestion.ladder_position is defined else -1 %}
+    {% if pos >= 0 %}
+    <div style="display: flex; gap: 0.25rem; align-items: center; margin-bottom: 0.75rem;">
+        {% for step in [6, 8, 10, 12] %}
+        <div style="flex: 1; text-align: center; padding: 0.35rem 0;
+                    border-radius: 0.25rem; font-size: 0.85rem; font-weight: 600;
+                    {% if loop.index0 <= pos %}
+                    background: var(--pico-primary); color: var(--pico-primary-inverse);
+                    {% else %}
+                    background: var(--pico-muted-border-color); color: var(--pico-muted-color);
+                    {% endif %}">
+            {{ step }}
         </div>
+        {% endfor %}
+        <small style="margin-left: 0.5rem; white-space: nowrap;">@ {{ suggestion.suggested_weight }}</small>
     </div>
+    {% else %}
+    <p><small>Starting weight: {{ program.starting_weight }}</small></p>
+    {% endif %}
     {% endif %}
 
     {% if suggestions and suggestions[exercise.id] %}