Expose every Bulma variant as a choosable option, not just a curated few

Adds a shared bulma_variants.py (color/size option lists) and expands BULMA_*_CONTROLS in bulma_controls.py to cover each component's full modifier set: Bouton (colour incl. white/light/dark/black/text, light-shade toggle, size, rounded, outlined, inverted, static, loading, fullwidth), Titre (Bulma size is-1..is-6 independent of heading level, is-spaced), Jauge (size), Tableau (bordered/fullwidth/striped/hoverable/narrow, now toggleable instead of hardcoded), Onglets (alignment, boxed/toggle/toggle-rounded style, size, fullwidth), and every form field — champ_texte/email/mot_de_passe, zone_texte, liste_deroulante (colour, size, rounded, static).

render_select.py/render_onglets.py/render_jauge.py now redirect the merged "class" from _visible_attrs to the actual Bulma sub-element (the .select wrapper, the .tabs div, the <progress> tag) instead of the outer positioning wrapper, since that's what needs to carry the modifier classes.

Also fixed a real latent bug found while wiring this up: a checkbox control with default=True (e.g. Tableau's "Première ligne = en-tête") was never actually applied on a freshly created element — default_style_and_attributes unconditionally skipped ALL checkbox types at creation, so the panel showed it checked while the element itself had nothing set. Now a checkbox's default=True is frozen at creation like any other meaningful default; default=False (the common case) is unaffected.

Verified end to end: every widget's variant controls save and render the right class tokens (spot-checked titre/tableau/onglets/champ_texte/liste_deroulante/jauge), full suite green (89 passed).

screens/rendering/render_jauge.py

@@ -138,8 +138,10 @@ def _render_jauge(el, meta, slug, children_map=None, ctx=None, parent_flex_direc
     # donnée" — sinon la jauge resterait figée sur sa valeur de départ après
     # un changement, exactement comme il fallait déjà repérer "repeaterItem"
     # pour les Répéteurs (voir 1.1/1.2).
+    extra_classes = " ".join(v for k, v in attrs.items() if k.startswith("_class_") and v)
+    bar_class = html_lib.escape((f"progress jaugeBar {extra_classes}").strip())
     bar = (
-        f'<progress class="progress jaugeBar" value="{percent}" max="100" '
+        f'<progress class="{bar_class}" value="{percent}" max="100" '
         f'style="--bulma-progress-value-background-color:{fill_color}; --bulma-progress-bar-background-color:#1c2130; '
         f'margin:0; border-radius:6px; transition:background-color .3s ease;">{percent}%</progress>'
     )