Codebase hardening: 102 fixes across 35+ files

Deep audit identified 106 findings; 102 fixed, 4 deferred. Covers 8 areas:

- Settings & deploy: env-gated DEBUG/SECRET_KEY, HTTPS headers, gunicorn, celery worker
- Auth (registered_user): password write_only, request.data fixes, transaction safety, proper HTTP status codes
- Workout app: IDOR protection, get_object_or_404, prefetch_related N+1 fixes, transaction.atomic
- Video/scripts: path traversal sanitization, HLS trigger guard, auth on cache wipe
- Models (exercise/equipment/muscle/superset): null-safe __str__, stable IDs, prefetch support
- Generator views: helper for registered_user lookup, logger.exception, bulk_update, transaction wrapping
- Generator core (rules/selector/generator): push-pull ratio, type affinity normalization, modality checks, side-pair exact match, word-boundary regex, equipment cache clearing
- Generator services (plan_builder/analyzer/normalizer): transaction.atomic, muscle cache, bulk_update, glutes classification fix

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

superset/models.py

@@ -14,9 +14,9 @@ class Superset(models.Model):
       related_name='superset_workout'
     )
 
-    rounds = models.IntegerField(max_length=3, blank=False, null=False)
-    order = models.IntegerField(max_length=3, blank=False, null=False)
-    estimated_time = models.FloatField(max_length=255, blank=True, null=True)
+    rounds = models.IntegerField(blank=False, null=False)
+    order = models.IntegerField(blank=False, null=False)
+    estimated_time = models.FloatField(blank=True, null=True)
     rest_between_rounds = models.IntegerField(default=45, help_text='Rest between rounds in seconds')
 
     def __str__(self):
@@ -39,10 +39,10 @@ class SupersetExercise(models.Model):
       related_name='superset_exercises'
     )
 
-    weight = models.IntegerField(null=True, blank=True, max_length=4)
-    reps = models.IntegerField(null=True, blank=True, max_length=4)
-    duration = models.IntegerField(null=True, blank=True, max_length=4)
-    order = models.IntegerField(max_length=3, blank=False, null=False)
+    weight = models.IntegerField(null=True, blank=True)
+    reps = models.IntegerField(null=True, blank=True)
+    duration = models.IntegerField(null=True, blank=True)
+    order = models.IntegerField(blank=False, null=False)
    
     def __str__(self):
         return self.superset.workout.name + " -- " + self.exercise.name