Design & Add a Dedicated Landing-Page Icon for the Nebari Chat Pack

[jbouder]

Summary

The Nebari chat pack renders a "Chat" card on the Nebari landing page via the landingPage block in helm/nebari-chat/values.yaml. That block sets displayName, description, category, priority, and healthCheck but leaves icon unset, so the card falls back to the generic Nebari logo. This issue covers designing a chat-specific icon and wiring it into the chart.

Motivation

• The card currently shows the generic Nebari fallback logo, making it visually indistinguishable from other un-iconed services
• The chart already supports the field — helm/nebari-chat/templates/_helpers.tpl renders icon and values.schema.json permits it — only the asset and value are missing
• A recognizable chat/AI icon improves scannability of the landing page as more packs are added
• Brings the chat pack in line with packs that will ship dedicated icons

Acceptance Criteria

• A chat-themed icon is designed as an .svg (with light/dark variants if the glyph needs them) and committed to the chart (e.g. helm/nebari-chat/assets/) or published at a stable URL
• helm/nebari-chat/values.yaml sets landingPage.icon (and iconLight/iconDark if separate variants exist) to reference the new asset
• helm/nebari-chat/templates/_helpers.tpl renders the chosen icon field(s) correctly
• helm/nebari-chat/values.schema.json allows the icon field(s) used
• helm template output shows the icon value in the rendered NebariApp
• Card verified on the landing page in both light and dark mode

Out of Scope

• Changes to landing-page rendering / icon-resolution logic in the nebari-landing repo
• Re-tuning other landingPage defaults (displayName, category, priority, healthCheck) — they are already set
• Application UI/in-app iconography unrelated to the landing-page card