feat(credits): solde IA unique (option M), packs Stripe et polish billing

Un pot de crédits global (BASIC 100 / PRO 1 000 / BUSINESS 4 000) remplace
les seaux par fonction côté débit. Packs one-shot S/M/L, admin sans seaux
legacy, usage multi-features, hints de coût, anti-flash thème et hydratation
admin. Inclut aussi le pipeline slides renforcé et la page publique polishée.

memento-note/lib/plan-entitlements.ts

@@ -19,6 +19,9 @@ export const FALLBACK_TIER_LIMITS: Record<
     brainstorm_expand: 10,
     brainstorm_enrich: 20,
     suggest_charts: 5,
+    // Multi-step pipeline charges ~4–9 units per deck → low monthly budget
+    slide_generate: 10,
+    excalidraw_generate: 5,
     ai_flashcard: 5,
     voice_transcribe: 20,
     publish_enhance: 2,
@@ -33,8 +36,9 @@ export const FALLBACK_TIER_LIMITS: Record<
     brainstorm_expand: 100,
     brainstorm_enrich: 200,
     suggest_charts: 50,
-    slide_generate: 20,
-    excalidraw_generate: 20,
+    // ~7 units/deck → ~20 decks/month at 140 units
+    slide_generate: 140,
+    excalidraw_generate: 40,
     ai_flashcard: 100,
     voice_transcribe: 500,
     publish_enhance: 15,
@@ -49,8 +53,9 @@ export const FALLBACK_TIER_LIMITS: Record<
     brainstorm_expand: 500,
     brainstorm_enrich: 1000,
     suggest_charts: 200,
-    slide_generate: 100,
-    excalidraw_generate: 100,
+    // ~7 units/deck → ~70 decks/month
+    slide_generate: 500,
+    excalidraw_generate: 200,
     ai_flashcard: 'unlimited',
     voice_transcribe: 'unlimited',
     publish_enhance: 100,