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/pages/schedule.html

@@ -1,50 +0,0 @@
-{% extends "base.html" %}
-
-{% block title %}4-Week Schedule -- SneakySwole{% endblock %}
-
-{% block content %}
-<hgroup>
-    <h1>4-Week Schedule</h1>
-    {% if active_profile %}
-    <p>Schedule for: <strong>{{ active_profile.display_name }}</strong></p>
-    {% else %}
-    <p>No profile selected -- <a href="/profiles">select one</a></p>
-    {% endif %}
-</hgroup>
-
-{% for week in weeks %}
-<article>
-    <header>
-        <h3>Week {{ week.week_number }}</h3>
-    </header>
-    <div class="grid">
-        {% for day in week.days %}
-        <div style="text-align:center;
-                    padding:1rem;
-                    border-radius:0.5rem;
-                    {% if day.is_today %}
-                    border: 2px solid var(--pico-primary);
-                    {% endif %}
-                    {% if day.is_completed %}
-                    background: rgba(99, 102, 241, 0.15);
-                    {% endif %}">
-            <strong>{{ day.workout_day.name }}</strong>
-            <br>
-            <small>{{ day.date.strftime('%b %d') }}</small>
-            {% if day.is_completed %}
-            <br><mark>Done</mark>
-            {% endif %}
-            {% if day.is_today %}
-            <br><small><strong>Today</strong></small>
-            {% endif %}
-            <br>
-            <a href="/workouts/{{ day.workout_day.name|lower|replace(' ', '-') }}"
-               style="font-size:0.8rem;">
-                Start
-            </a>
-        </div>
-        {% endfor %}
-    </div>
-</article>
-{% endfor %}
-{% endblock %}