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/log_form.html

@@ -12,8 +12,13 @@
         <input type="number" name="reps" placeholder="Reps"
                min="0" max="100" required
                style="width:5rem; margin-bottom:0;">
-        <input type="text" name="weight" placeholder="Weight (lbs)"
-               required
+        <input type="number" name="weight" placeholder="Weight (lbs)"
+               min="0" max="999" step="0.5" required
+               {% if suggested_weight and suggested_weight != "BW" %}
+               value="{{ suggested_weight|replace(' lbs', '') }}"
+               {% elif suggested_weight == "BW" %}
+               value="0"
+               {% endif %}
                style="width:8rem; margin-bottom:0;">
         <label style="display:flex; align-items:center; gap:0.3rem; margin-bottom:0; white-space:nowrap;">
             <input type="checkbox" name="felt_easy" role="switch" style="margin-bottom:0;">