docs: describe AI-assisted development, add Sidebar example, other improvements

[pkosiec]

This PR addresses the agentic feedback from @arsenyinfo - all points except #9. Why? Lakebase setup is manual for now until there's Apps x Lakebase v2 native integration.

Issues / Gaps

  High priority:

  1. No useAnalyticsQuery hook documentation visible — This is the primary frontend data-fetching primitive, referenced everywhere (LLM guide, type generation, charts), but I couldn't find a standalone doc page for it. An agent trying to wire up a query would have to guess the API
  or read chart component docs hoping for clues.
  2. Sidebar docs lack composition example — 23 sub-components documented individually, but no example showing how to compose them together (SidebarProvider → Sidebar → SidebarContent → SidebarGroup → SidebarMenu → SidebarMenuItem → SidebarMenuButton). An LLM will struggle to
  produce a working sidebar without a full example.
  3. createApp reference is thin — No description of what happens during initialization, no examples showing common plugin combinations, no explanation of PluginMap return type. The most important function in the SDK deserves more.
  4. AI-assisted development page is a stub — "Coming soon" is fine for humans, but an LLM that lands here wastes a tool call and gets no value.

  Medium priority:

  5. No end-to-end example — There's no single page showing a complete mini-app (backend query + frontend hook + chart rendering). The pieces are documented separately but never assembled. This is what agents need most for code generation tasks.
  6. Plugin exports() pattern not in plugin reference — The custom plugins guide shows it, but the Plugin class API reference likely doesn't emphasize this critical pattern. Agents reading only the API docs would miss it.
  7. No error handling patterns — LLM guide says "always handle loading/error/empty states" but doesn't show how. What does useAnalyticsQuery return for error states? What does a failed query look like?
  8. useSidebar hook has wrong Usage block — Shows <useSidebar /* props */ /> as JSX, which is nonsensical for a hook. Copy-paste bug from the doc generator.

  Low priority:

  9. Lakebase setup is very manual — Not a docs quality issue per se, but the 6-step manual SQL setup is a lot for an LLM to guide a user through. The docs handle it well though.
  10. Some prop descriptions are empty — Sidebar side, variant, collapsible have no description, just types with defaults. An agent can't explain what variant: "sidebar" vs other options means.

  Agentic Readiness Score: 7/10

Resolves https://databricks.atlassian.net/browse/LKB-9342

Screenshots