chore: remove legacy Windows launcher and PORTABLE verification records

Storybook is served on the web (main deployment), so the Windows BAT
launcher and its Node helper are no longer used. The root PORTABLE
r4-r6 verification records are historical ZIP-era notes that nothing
references.

- Delete start-storybook.bat and scripts/start-storybook.mjs
- Delete PORTABLE-R4/R5-CANDIDATE/R5/R6-VERIFICATION.md
- README, publisher distribution guide, LAN preview note: point to the
  web Storybook; keep npm run storybook for local development
- v2 baseline report: unlink the removed files, keep the record text

.storybook/qa/LAN-PREVIEW.md

@@ -1,6 +1,6 @@
 # Track B temporary Storybook LAN preview
 
-> Historical scope: the Track B session below was verified on 2026-10-07. Ordinary users should follow the [official source installation guide](../../docs/guidelines/publisher-distribution-guide.md) and use `npm run storybook` or `start-storybook.bat` at the repository root; the current default port is **6024**. LAN Preview is optional internal QA. The old 6007 package port and the temporary 6008 session are historical observations. No server binding, network profile or firewall configuration is changed by this documentation update.
+> Historical scope: the Track B session below was verified on 2026-10-07. Ordinary users should follow the [official source installation guide](../../docs/guidelines/publisher-distribution-guide.md) and use the web Storybook or `npm run storybook` at the repository root; the current default port is **6024**. LAN Preview is optional internal QA. The old 6007 package port and the temporary 6008 session are historical observations. No server binding, network profile or firewall configuration is changed by this documentation update.
 
 Purpose: **TEMPORARY INTERNAL LAN PREVIEW / LAN TEMP PREVIEW** for Storybook cleanup. This is a development server with HMR, not official static hosting or a permanent URL.