Refresh the getting started pages and homepage

[andygrillo]

What changed

• Start Here: new "When your sensors arrive" walkthrough. Pulse/One: invitation, claim by Device ID or QR (factory-registered), power and connect, online in the list. Slide: Grillo Field on Android, SIM and APN, install and survey, first readings. Path table adds Add Colleagues and Slide exports. Notes that Grillo sets up accounts in both dashboards.
• What Is Grillo?: QR claiming, Slide exports and over-the-air firmware, a Grillo Field app section (iPhone coming soon), data routing to your own server set up by Grillo, and the chat messenger.
• Choosing Your Sensor: comparison adds readings (continuous vs every 6 hours), what each dashboard shows, and firmware updates; One mentions USB-C; Slide needs no mains or network at the site.
• Homepage: checklist mentions the QR code and the Slide base survey; help points to the chat messenger.

npm run build passes.

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