fix: hide .notes from slides + add explicit no-presenter-text rule

- base.css: add .notes{display:none!important} so speaker notes are never
  visible on the rendered slide (only in S overlay)
- SKILL.md: add NEVER-put-presenter-text rule in authoring rules
- authoring-guide.md: add same rule in What to NOT do section

Fixes issue where AI would put small descriptive/presenter-only text
directly on slide markup instead of inside <div class='notes'>.

SKILL.md

@@ -113,6 +113,12 @@ Only after those are clear, scaffold the deck and start writing.
   visible; all others are hidden.
 - **Supply notes.** Wrap speaker notes in `<div class="notes">…</div>` inside
   each slide. Press S to open the overlay.
+- **NEVER put presenter-only text on the slide itself.** Descriptive text like
+  "这一页展示了……" or "Speaker: 这里可以补充……" or small explanatory captions
+  aimed at the presenter MUST go inside `<div class="notes">`, NOT as visible
+  `<p>` / `<span>` elements on the slide. The `.notes` class is `display:none`
+  by default — it only appears in the S overlay. Slides should contain ONLY
+  audience-facing content (titles, bullet points, data, charts, images).
 
 ## Writing guide
 

assets/base.css

@@ -116,6 +116,7 @@ h4,.h4{font-size:22px;line-height:1.3;font-weight:600;margin:0 0 8px}
 .progress-bar > span{display:block;height:100%;width:0;background:var(--accent);transition:width .3s var(--ease)}
 
 /* ================= PRESENTER / OVERVIEW ================= */
+.notes{display:none!important}
 .notes-overlay{position:fixed;inset:auto 0 0 0;max-height:42vh;background:rgba(20,22,30,.95);color:#e8ebf4;
   padding:20px 32px;font-size:16px;line-height:1.6;border-top:1px solid rgba(255,255,255,.1);transform:translateY(100%);
   transition:transform .3s var(--ease);z-index:40;overflow:auto;font-family:var(--font-sans)}

references/authoring-guide.md

@@ -123,6 +123,12 @@ for 小红书图文 (1242×1660).
 - Don't add more than one new template file unless a genuinely new layout
   type is needed. Prefer composition.
 - Don't delete slides from the showcase decks.
+- **Don't put presenter-only text on the slide.** Any descriptive text,
+  narration cues, or explanations meant for the speaker (e.g. "这一页的重点是…",
+  "Note: mention X here", small grey captions explaining the slide's purpose)
+  MUST go inside `<div class="notes">`, not as visible elements. The `.notes`
+  div is hidden (`display:none`) and only shown via the S overlay. Slides
+  should contain ONLY audience-facing content.
 
 ## Troubleshooting