Rework docs navigation and move alternatives to top-level pages (#1487)

* Rework docs navigation and move alternatives to top-level pages

- Add nested docs nav with categories, collapsible groups, breadcrumbs,
  and a right-hand page outline with heading slugs.
- Move alternatives out of /docs/alternatives into /alternatives/*
  marketing pages with 301 redirects.
- Add github-slugger for heading IDs and require explicit width on
  SiteShell so new pages can't accidentally pick the narrow prose layout.
- Remove the best-practices doc from public-docs.

* Make docs content column prose-width

packages/website/src/routes/alternatives/claude-desktop.tsx

@@ -0,0 +1,6 @@
+import { createFileRoute } from "@tanstack/react-router";
+import { alternativeRouteOptions } from "~/components/alternative-page";
+
+export const Route = createFileRoute("/alternatives/claude-desktop")(
+  alternativeRouteOptions("claude-desktop"),
+);

packages/website/src/routes/alternatives/codex-app.tsx

@@ -0,0 +1,6 @@
+import { createFileRoute } from "@tanstack/react-router";
+import { alternativeRouteOptions } from "~/components/alternative-page";
+
+export const Route = createFileRoute("/alternatives/codex-app")(
+  alternativeRouteOptions("codex-app"),
+);

packages/website/src/routes/alternatives/conductor.tsx

@@ -0,0 +1,6 @@
+import { createFileRoute } from "@tanstack/react-router";
+import { alternativeRouteOptions } from "~/components/alternative-page";
+
+export const Route = createFileRoute("/alternatives/conductor")(
+  alternativeRouteOptions("conductor"),
+);

packages/website/src/routes/alternatives/happy-coder.tsx

@@ -0,0 +1,6 @@
+import { createFileRoute } from "@tanstack/react-router";
+import { alternativeRouteOptions } from "~/components/alternative-page";
+
+export const Route = createFileRoute("/alternatives/happy-coder")(
+  alternativeRouteOptions("happy-coder"),
+);

packages/website/src/routes/alternatives/openchamber.tsx

@@ -0,0 +1,6 @@
+import { createFileRoute } from "@tanstack/react-router";
+import { alternativeRouteOptions } from "~/components/alternative-page";
+
+export const Route = createFileRoute("/alternatives/openchamber")(
+  alternativeRouteOptions("openchamber"),
+);

packages/website/src/routes/alternatives/opencode-desktop.tsx

@@ -0,0 +1,6 @@
+import { createFileRoute } from "@tanstack/react-router";
+import { alternativeRouteOptions } from "~/components/alternative-page";
+
+export const Route = createFileRoute("/alternatives/opencode-desktop")(
+  alternativeRouteOptions("opencode-desktop"),
+);

packages/website/src/routes/alternatives/superset.tsx

@@ -0,0 +1,4 @@
+import { createFileRoute } from "@tanstack/react-router";
+import { alternativeRouteOptions } from "~/components/alternative-page";
+
+export const Route = createFileRoute("/alternatives/superset")(alternativeRouteOptions("superset"));