v0.4.0-alpha: duplicate_demo, editor UI for branches/chapters, delete, personalized links

- duplicate: REST + MCP tool + editor button. Deep copy with branch targets
  and chapter targets remapped into the copy; lead gates + raster cache
  carried; copy is always a private draft (no inherited share token).
  Verified: 3 steps / 2 chapters / 1 branch all internally consistent.
- delete demo: REST + editor button; FK cascade verified (0 orphans)
- Editor: draw-mode toggle (hotspot vs branch) with target-step picker and
  branch list; chapters manager panel; personalized-link generator;
  duplicate/delete on demo list
- MCP surface: 16 tools
- USER-GUIDE updated: new editor features + personalization prompt now uses
  duplicate_demo

docs/USER-GUIDE.md

@@ -76,6 +76,15 @@ are the last line of defence.
 - **Lead gate** — tick the box on a step and viewers must leave name + email
   before advancing past it. Put it after you've shown value, not on step 1
 - **Reorder / delete** — arrows and × in the step list
+- **Branch hotspots** — switch Draw mode to "Branch", drag a region, pick the
+  target step. Branches render dashed in the player and let viewers choose
+  their own path
+- **Chapters** — the Chapters panel in the sidebar builds the jump menu shown
+  in the player bar
+- **Duplicate / delete demos** — ⧉ and × on the demo list. Duplicate before
+  personalizing for a prospect; the copy is always a private draft
+- **Personalized link** — one click generates a share link with a viewer token
+  baked in
 - **Step guide** — auto-generated from your steps at `/p/<token>/guide`
 - **Export video** — renders an MP4 slideshow of all steps; add narration via
   your agent (§7, "Narrated video")
@@ -138,10 +147,11 @@ the agent can list them.
 > "Deep dive", "Getting started".
 
 **Personalized prospect demo:**
-> Duplicate isn't available yet, so: take demo "Generic Tour" and rewrite all
-> tooltips to speak directly to Acme Corp (logistics company, 400 trucks,
-> pain point is manual dispatch). Mention their industry where natural. Give
-> me the personalized share link format with viewer token acme-corp.
+> Duplicate the demo "Generic Tour", then rewrite all tooltips in the copy to
+> speak directly to Acme Corp (logistics company, 400 trucks, pain point is
+> manual dispatch). Mention their industry where natural. Rename the copy
+> "Acme Corp Tour" and tell me when it's ready to publish — I'll send it with
+> viewer token acme-corp.
 
 **Branching demo (choose-your-own path):**
 > On demo "Full Product Tour": add branch hotspots on step 1 — one labeled