docs: migrate webdocs from Mintlify to fumadocs content format

[aroff]

Summary

• Migrate all 49 MDX/MD files in webdocs/ from Mintlify components to fumadocs MDX format
• Replace central mint.json config with 13 per-folder meta.json navigation files
• Convert all Mintlify-specific components to fumadocs equivalents (Callouts, Cards, Accordions, Steps, Tabs, ParamField)
• Add MIGRATION.md documenting the conversion and host-app integration steps

Component mappings

Mintlify	Fumadocs
<Note>/<Info>/<Warning>/<Tip>/<Check>	<Callout type="...">
<CardGroup>/<Card icon="...">	<Cards>/<Card>
<AccordionGroup>/<Accordion>	<Accordions>/<Accordion id="...">
<Steps>/<Step title="X">	### 1. X numbered headings
<Tabs>/<Tab title="X">	<Tabs items={[...]}>/<Tab value="X">
<ParamField>	#### \field` (type, required)` headings
<Frame>	removed (content kept)

Validation

All 15 key pages verified with Playwright headless browser testing:

• 15/15 pages return HTTP 200 with correct h1 titles
• Sidebar navigation (290px aside with all groups/links) rendering correctly
• Tabs, Cards, Callouts, Accordions, and Steps components all rendering
• All screenshots unique (no duplicate/blank captures)
• CSS theme loading properly (84KB compiled stylesheet)

This migration covers content only — no hosting application is included. The converted content drops into any fumadocs MDX app by pointing defineDocs({ dir: 'content/docs' }) at this directory.