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/services/seed_service.py

@@ -157,10 +157,7 @@ class SeedService:
                 uep = UserExerciseProgram(
                     user_id=user.id,
                     exercise_id=exercise.id,
-                    wk1_reps=str(ex_data.get("wk1_reps", "")),
-                    wk4_reps=str(ex_data.get("wk4_reps", "")),
-                    wk1_weight=str(ex_data.get("wk1_weight", "")),
-                    wk4_weight=str(ex_data.get("wk4_weight", "")),
+                    starting_weight=str(ex_data.get("starting_weight", "")),
                 )
                 self._session.add(uep)