docs: lowercase internal docs + migrate website docs to public-docs/ (#634)

* docs: rename to lowercase + drop leftover plans

Rename docs in docs/ to lowercase kebab-case for consistency and update
all references in CLAUDE.md, CONTRIBUTING.md, CHANGELOG.md,
packages/server/CLAUDE.md, and inter-doc links.

Drop two leftover design plan docs:
- docs/ATTACHMENT_BASED_REVIEW_CONTEXT_PLAN.md
- docs/plan-approval-normalization.md

* docs: drop stale uppercase entries from case-insensitive rename

* feat(website): power /docs from public-docs/ markdown tree

Move website docs out of TSX route components and into a root-level
public-docs/ directory of plain markdown files with frontmatter
(title, description, nav, order).

- Add packages/website/src/docs.ts loader using import.meta.glob with
  ?raw to compile the markdown into the bundle at build time.
- Replace the 9 hand-written docs/*.tsx routes with a single $.tsx
  catch-all that renders any slug via react-markdown.
- Drive the docs sidebar nav from frontmatter order/nav.
- Auto-discover docs routes in vite.config.ts so the sitemap stays in
  sync without manual edits.

* fix(website): bind dev server to 0.0.0.0 so port collisions trigger fallback

`host: "127.0.0.1"` (or unset) lets macOS coexist with another process
holding an IPv6 dual-stack `*:8082` socket, so Vite never sees
EADDRINUSE and silently binds alongside it. Forcing IPv4 wildcard
makes the conflict real, and Vite's default `strictPort: false`
falls through to the next free port.

* fix(website): restore docs page styling after markdown migration

Add a .docs-prose class that mirrors the styling the original
docs/*.tsx components hand-rolled (h1/h2/h3 sizes, paragraph/list
spacing, link colors, code blocks, callout-style blockquotes).

ReactMarkdown was emitting unstyled HTML because the previous
wrapper class only had inline-code rules — headings and code
blocks fell back to user-agent defaults.

CHANGELOG.md

@@ -207,7 +207,7 @@
 
 ### Added
 
-- Provider profiles — define custom providers in your Paseo config that appear alongside built-ins. Override a built-in's binary, env, or models, or create entirely new providers. See the [configuration guide](https://github.com/getpaseo/paseo/blob/main/docs/CUSTOM-PROVIDERS.md).
+- Provider profiles — define custom providers in your Paseo config that appear alongside built-ins. Override a built-in's binary, env, or models, or create entirely new providers. See the [configuration guide](https://github.com/getpaseo/paseo/blob/main/docs/custom-providers.md).
 - ACP agent support — add any ACP-compatible agent to Paseo with `extends: "acp"` in your provider config. No code changes needed.
 - Choose provider and model when creating scheduled agents.
 - Max reasoning effort option for Opus 4.6 models.