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/progression_badge.html

@@ -1,6 +1,15 @@
 {% if suggestion and suggestion.progression_type != "no_program" %}
+{% set badge_colors = {
+    "deload": "var(--pico-del-color)",
+    "weight_increase": "var(--pico-ins-color)",
+    "climb": "var(--pico-primary)",
+    "hold": "var(--pico-muted-color)",
+    "hold_at_top": "var(--pico-muted-color)",
+    "baseline": "var(--pico-primary)",
+} %}
+{% set border_color = badge_colors.get(suggestion.progression_type, "var(--pico-primary)") %}
 <div style="background: rgba(99, 102, 241, 0.1);
-            border-left: 3px solid var(--pico-primary);
+            border-left: 3px solid {{ border_color }};
             padding: 0.5rem 1rem;
             margin-bottom: 0.5rem;
             border-radius: 0 0.25rem 0.25rem 0;">