add Minikube section to CE-to-PE upgrade guide and fix license key in…

[epalchenko]

Description

Add Minikube upgrade path to the CE-to-PE upgrade guide.

The upgrade-from-ce page had no Kubernetes steps. Adds a Minikube section covering the full flow: stop CE resources, clone the PE scripts repository, configure the license key, run the database upgrade, and deploy PE resources.

Also fixes the TB_LICENSE_SECRET description in minikube-cluster-setup.mdx the placeholder text referenced PUT_YOUR_LICENSE_SECRET_HERE, which does not exist in the actual tb-node.yml (the value field is empty by default).

Type of change

• New / updated documentation page (src/content/docs/**)
• Shared include file (src/content/_includes/**)
• Component, layout, or styling change (src/components/**, src/styles/**)
• Landing / use-case / case-study page (src/pages/**, src/data/**)
• Redirects (src/data/redirects.ts)
• Version bump / release (see release skill)
• Build, CI, scripts, or tooling
• Other (please describe)

Affected products

Related issues

• Closes #

Checklist

• pnpm check passes (Astro / TypeScript)
• pnpm lint:eslint passes
• pnpm lint:slugcheck passes (required if pages were added/renamed/moved across languages)
• pnpm lint:linkcheck passes locally — required to merge; run it before requesting review (use pnpm lint:linkcheck:nobuild if you already ran a build)
• Renamed/removed pages have a redirect in src/data/redirects.ts, and pnpm generate:redirects was run
• No hardcoded versions — values come from src/data/versions.ts
• Screenshots attached for visual changes