refactor(generator): 6-step wizard, one decision per page

The old step 2 was a vertedero: major levels, minor levels, feature
counts, tree depth, relation distribution slider, feature-cardinality
block and group-cardinality block — all on a single scroll-heavy page.
Step 1 also mixed batch basics (num_models/seed/prefix) with
post-processing options (ensure_satisfiable, filename suffixes).

New layout — every step answers exactly one question:

    1 Batch           num_models, seed, name_prefix
    2 Language levels major + minor toggles (pure expressivity)
    3 Feature tree    features/depth/relation dist + feat/group card
    4 Constraints     counts, vars/ctc, CTC_DIST + prob distributions
    5 Attributes      random/manual, DIST_BOOLEAN/INT/REAL/STRING
    6 Output          ensure_satisfiable, suffixes, download

Internals
- routes.py split into one validator per step (validate_step1..step6)
  plus one _apply_stepN_xxx persistor each. Each step only writes the
  fields it owns, so back-nav can't silently drop state from later
  steps.
- _apply_step2_levels now normalises TYPE_LEVEL \u2192 ARITHMETIC_LEVEL so the
  session always matches what Params.__post_init__ would produce.
- step2 UI script moved inside #stepper_generator so wizard-spa.js
  re-executes it on every SPA swap; the change handlers survive
  prev/next navigation.

Tests
- 367 generator tests green (13 engine + 22 validator + 140+ wizard
  output + 12 wizard flow + assorted contract/unit).
- 454 uvlhub tests green overall, 0 flake8 errors.

Author: drorganvidez

app/modules/generator/routes.py

@@ -51,11 +51,12 @@
 
 
 {% set steps = [
-    ('General information', 'Global settings'),
-    ('Feature tree', 'Structure and levels'),
+    ('Batch', 'Models, seed, name'),
+    ('Language levels', 'Pick the expressivity'),
+    ('Feature tree', 'Shape and relation mix'),
     ('Constraints', 'Cross-tree constraints'),
     ('Attributes', 'Attribute catalog'),
-    ('Finishing', 'Download your models')
+    ('Output', 'Final options & download')
 ] %}
 
 <div class="stepper stepper-pills stepper-column d-flex flex-column flex-xl-row flex-row-fluid gap-10" id="stepper_generator">
@@ -121,7 +122,7 @@ <h2 class="fw-bold text-gray-900">{{ steps[current_step - 1][0] }}</h2>
                         {% endif %}
                     </div>
                     <div>
-                        {% if current_step < 5 %}
+                        {% if current_step < 6 %}
                         <button type="submit"
                                 name="nav"
                                 value="next"

app/modules/generator/templates/generator/index.html

@@ -1,9 +1,16 @@
 {% extends "generator/index.html" %}
-{% from "generator/_macros.html" import info, number_field, check_field %}
+{% from "generator/_macros.html" import info, number_field %}
 
 {% block title %}Generate random feature models{% endblock %}
 
 {% block wizard_content %}
+<div class="notice d-flex bg-light-primary rounded border-primary border border-dashed p-5 mb-8">
+    <i class="ki-duotone ki-information fs-2x text-primary me-4 mt-1"><span class="path1"></span><span class="path2"></span><span class="path3"></span></i>
+    <div class="fs-7 text-gray-700 fw-semibold">
+        This first step is just the basics of the batch — how many models to produce, a seed for reproducibility, and a name prefix for the output files. Advanced options (language levels, tree shape, constraints, attributes, ensure-satisfiable, filename suffixes) come in later steps.
+    </div>
+</div>
+
 <div class="row g-8">
     <div class="col-xl-8">
 
@@ -18,28 +25,14 @@
         <div class="mb-7">
             <label for="name_prefix" class="form-label d-flex align-items-center">
                 Name prefix
-                {{ info("Prefix used when naming the generated UVL files (e.g. 'fm' produces fm_0.uvl, fm_1.uvl…).") }}
+                {{ info("Prefix used when naming the generated UVL files (e.g. 'fm' produces fm0.uvl, fm1.uvl…).") }}
             </label>
             <input type="text" id="name_prefix" name="name_prefix"
                    placeholder="fm"
                    value="{{ values.get('name_prefix', '') }}"
                    class="form-control form-control-solid">
         </div>
 
-        <div class="separator separator-dashed my-7"></div>
-
-        <div class="d-flex flex-column gap-4">
-            {{ check_field('ensure_satisfiable', 'Ensure satisfiable',
-                'If on, the generator rejects unsatisfiable models and keeps sampling until it gets a valid one.',
-                values) }}
-            {{ check_field('feature_count_suffix', 'Append feature count to filename',
-                "Adds '_Nf' to each filename, where N is the number of features of that model.",
-                values) }}
-            {{ check_field('constraint_count_suffix', 'Append constraint count to filename',
-                "Adds '_Nc' to each filename, where N is the number of cross-tree constraints of that model.",
-                values) }}
-        </div>
-
         {% if errors.get('global') %}
             <div class="alert alert-danger mt-7">{{ errors['global'] }}</div>
         {% endif %}