Make Jauge, Onglets, and every form-field widget real native Bulma elements

- Jauge now renders a real <progress class="progress"> instead of a hand-built pair of absolutely-positioned divs. The bas/haut color interpolation still works, set via Bulma's own --bulma-progress-value-background-color CSS custom property rather than fighting the class.
- Onglets' tab strip is now genuine Bulma tabs markup (tabs > ul > li, is-active on the li) instead of custom forgeTabBar/forgeTabBtn classes; forgeShowTab (duplicated in screen_edit.html and play.html) now toggles is-active to match.
- Champ texte/email/mot de passe get class="input", Zone de texte gets class="textarea", Case à cocher/Bouton radio's existing <label> wrapper gets class="checkbox"/"radio" (Bulma's own convention — the structure already matched, just needed the class), Liste déroulante is wrapped in Bulma's required <div class="select"> (a bare class on the <select> itself has zero effect in Bulma), Tableau gets class="table is-bordered is-fullwidth" with the per-cell inline borders removed so Bulma's own table styling applies.
- Removed the now-dead .forgeTabBar/.forgeTabBtn CSS.

Updated tests/test_jauge.py and tests/test_onglets_widget.py assertions to match the new markup (value="X" attribute instead of width:X% inline style, --bulma-progress-value-background-color instead of background-color, forgeShowTab(this) marker instead of the removed forgeTabBtn class) — same behavior, different rendering mechanism. Full suite green (89 passed), verified end to end against the real "test" project via the actual /play route.

static/style.css

@@ -254,14 +254,9 @@ body.builderBody > main.content{ flex:1 1 auto; min-height:0; overflow:hidden; d
 }
 .contextMenu button:hover{ background:var(--panel2); }
 
-/* Élément à onglets (voir render_onglets.py) */
-.forgeTabBar{ display:flex; flex-wrap:wrap; gap:2px; border-bottom:1px solid var(--border); }
-.forgeTabBtn{
-  background:none; border:none; border-bottom:2px solid transparent; color:var(--text-dim);
-  padding:8px 14px; font-size:14px; font-family:inherit; cursor:pointer; white-space:nowrap;
-}
-.forgeTabBtn:hover{ color:var(--text); }
-.forgeTabBtn.active{ color:var(--text); border-bottom-color:var(--accent); font-weight:600; }
+/* Élément à onglets (voir render_onglets.py) : la barre d'onglets elle-même
+   est un vrai composant Bulma ("tabs" > "ul" > "li", voir render_onglets.py)
+   — il ne reste ici que les panneaux, que Bulma n'a pas de composant pour. */
 .forgeTabPanels{ min-width:0; }
 .forgeTabPanel{ padding-top:10px; }