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/models/user_exercise_program.py

@@ -1,6 +1,6 @@
 """UserExerciseProgram model for per-user exercise programming.
 
-Links a user to an exercise with week 1 and week 4 rep/weight targets.
+Links a user to an exercise with a starting weight for the rep ladder.
 """
 
 from datetime import datetime
@@ -16,10 +16,7 @@ class UserExerciseProgram(SQLModel, table=True):
         id: Primary key, auto-incremented.
         user_id: FK to users table.
         exercise_id: FK to exercises table.
-        wk1_reps: Week 1 target reps (string to support "30 sec" style).
-        wk4_reps: Week 4 target reps.
-        wk1_weight: Week 1 target weight (e.g., "30 lbs", "BW").
-        wk4_weight: Week 4 target weight.
+        starting_weight: Starting weight (e.g., "30 lbs", "BW").
         created_at: Timestamp when the record was created.
         updated_at: Timestamp of the last update.
     """
@@ -29,9 +26,6 @@ class UserExerciseProgram(SQLModel, table=True):
     id: Optional[int] = Field(default=None, primary_key=True)
     user_id: int = Field(foreign_key="users.id", index=True)
     exercise_id: int = Field(foreign_key="exercises.id", index=True)
-    wk1_reps: str = Field(default="")
-    wk4_reps: str = Field(default="")
-    wk1_weight: str = Field(default="")
-    wk4_weight: str = Field(default="")
+    starting_weight: str = Field(default="")
     created_at: datetime = Field(default_factory=datetime.utcnow)
     updated_at: datetime = Field(default_factory=datetime.utcnow)