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/components/publish/reading-progress.tsx

@@ -0,0 +1,77 @@
+'use client'
+
+import { useEffect, useState } from 'react'
+
+/**
+ * Thin reading progress bar. Tracks the nearest scrollable ancestor
+ * (public layout uses a fixed-height overflow container, not window).
+ */
+export function ReadingProgress({ accent = '#A47148' }: { accent?: string }) {
+  const [progress, setProgress] = useState(0)
+
+  useEffect(() => {
+    const findScrollRoot = (): HTMLElement | Window => {
+      let el: HTMLElement | null = document.querySelector('[data-pub-root]') as HTMLElement | null
+      while (el) {
+        const { overflowY } = getComputedStyle(el)
+        if (overflowY === 'auto' || overflowY === 'scroll') return el
+        el = el.parentElement
+      }
+      return window
+    }
+
+    const root = findScrollRoot()
+
+    const update = () => {
+      let scrollTop: number
+      let scrollHeight: number
+      let clientHeight: number
+      if (root === window) {
+        scrollTop = window.scrollY
+        scrollHeight = document.documentElement.scrollHeight
+        clientHeight = window.innerHeight
+      } else {
+        const node = root as HTMLElement
+        scrollTop = node.scrollTop
+        scrollHeight = node.scrollHeight
+        clientHeight = node.clientHeight
+      }
+      const max = Math.max(1, scrollHeight - clientHeight)
+      setProgress(Math.min(100, Math.max(0, (scrollTop / max) * 100)))
+    }
+
+    update()
+    root.addEventListener('scroll', update, { passive: true })
+    window.addEventListener('resize', update, { passive: true })
+    return () => {
+      root.removeEventListener('scroll', update)
+      window.removeEventListener('resize', update)
+    }
+  }, [])
+
+  return (
+    <div
+      aria-hidden
+      style={{
+        position: 'fixed',
+        top: 0,
+        left: 0,
+        right: 0,
+        height: 3,
+        zIndex: 100,
+        background: 'transparent',
+        pointerEvents: 'none',
+      }}
+    >
+      <div
+        style={{
+          height: '100%',
+          width: `${progress}%`,
+          background: accent,
+          boxShadow: `0 0 12px ${accent}66`,
+          transition: 'width 80ms linear',
+        }}
+      />
+    </div>
+  )
+}