fix(setup): pin Baileys to 7.0.0-rc.9 in install-whatsapp scripts

PR #2259 (Baileys v6→v7) was merged into the channels branch instead of
main. PR #2260 was merged into main 28s later assuming v7 was already
in place. The v6 pin survived in three sites while the WhatsApp adapter
copied from origin/channels at install time was already on the v7 LID
API, breaking every fresh migrate-v2.sh run at 2c-install-whatsapp with
TS errors on remoteJidAlt/participantAlt/lid-mapping.update.

Bumps the pin to 7.0.0-rc.9 (the version v1 has been running on for
months) in:

- setup/install-whatsapp.sh
- setup/add-whatsapp.sh
- .claude/skills/add-whatsapp/SKILL.md (install instruction)

package.json + pnpm-lock.yaml are not touched here — install-whatsapp.sh
mutates them at runtime via pnpm install with the corrected pin.

Closes #2283

.claude/skills/add-whatsapp/SKILL.md

@@ -57,7 +57,7 @@ groups: () => import('./groups.js'),
 ### 5. Install the adapter packages (pinned)
 
 ```bash
-pnpm install @whiskeysockets/baileys@6.17.16 qrcode@1.5.4 @types/qrcode@1.5.6 pino@9.6.0
+pnpm install @whiskeysockets/baileys@7.0.0-rc.9 qrcode@1.5.4 @types/qrcode@1.5.6 pino@9.6.0
 ```
 
 ### 6. Build