docs: introduce versioned docs and migrate to fuma (#11166)

## Todos for release

- [x] Configure Env in docs project on vercel
- [x] Configure Root Path in the docs project on vercel
- [ ] Remove old CSP https://github.com/zitadel/website/pull/1592

## What we did

This pull request migrates the project documentation from the old
`docs/` directory to the new `apps/docs/` directory, introduces a new
documentation system built with Next.js and Fumadocs, and updates all
relevant references, configuration files, and documentation to reflect
this change. It also adds new configuration and ignore files for the new
documentation app, updates CI and linting to exclude the new docs from
certain checks, and revises the contributing guidelines accordingly.

**Documentation System Migration and New Docs App**

* Migrated all documentation from `docs/` to `apps/docs/`, and updated
all references in `README.md`, `CONTRIBUTING.md`, and other files to
point to the new location.
[[1]](diffhunk://#diff-eca12c0a30e25b4b46522ebf89465a03ba72a03f540796c979137931d8f92055L585-L640)
[[2]](diffhunk://#diff-eca12c0a30e25b4b46522ebf89465a03ba72a03f540796c979137931d8f92055L660-R607)
[[3]](diffhunk://#diff-eca12c0a30e25b4b46522ebf89465a03ba72a03f540796c979137931d8f92055L740-R687)
[[4]](diffhunk://#diff-b335630551682c19a781afebcf4d07bf978fb1f8ac04c6bf87428ed5106870f5L2-R3)
[[5]](diffhunk://#diff-b335630551682c19a781afebcf4d07bf978fb1f8ac04c6bf87428ed5106870f5L30-R30)
* Added a new Next.js/Fumadocs-based documentation app under
`apps/docs/`, including core app files, layouts, routing, search API,
and a comprehensive `README.md` with development and contribution
instructions.
[[1]](diffhunk://#diff-5a1b07344a2c1b4d3f37b23ff1388b62cd9f57dea3c1cd23d8a0412b7602b132R1-R74)
[[2]](diffhunk://#diff-462b9ad1eabbb7d1c29bb9c36e4931eb180fd7190900e6d2babf8f4d66ad1c28R1-R39)
[[3]](diffhunk://#diff-e16ae25660ded787b10ac35dea96d5ecaacf895dae0afc8a9bd4382dc79a8c87R1-R7)
[apps/docs/app/[[...slug]]/layout.tsxR1-R81](diffhunk://#diff-59e08acde4e805b7aeccef1dcf98f1d71dfc550777e6b9402085cee0e9fa4e0aR1-R81),
[apps/docs/app/[[...slug]]/page.tsxR1-R79](diffhunk://#diff-e5df3f80d0fa01e12d63d81f29c57a9d14e846c78fd3beabb2ef768e38fd9580R1-R79),
[[4]](diffhunk://#diff-389b34918e040cacaa87cd7201ffa462cc2b0b716736f537e3d3c660ac69353bR1-R7)
[[5]](diffhunk://#diff-d3b03416d1c457b19f1c27b26f2db741412df841b875c26ccadc36e4522247f4R1-R29)
[[6]](diffhunk://#diff-c8fb8339570a5305809be7c618e14705fd86390dc278e6ce8ba224a7bc8b0c3cR1-R25)

**Configuration and Tooling Updates**

* Updated `.github/workflows/codeql.yml`, `.golangci.yaml`, and
`.github/dependabot.yml` to properly handle the new docs app: excluded
`apps/docs` from certain checks, added npm dependency updates for the
docs app, and excluded generated content.
[[1]](diffhunk://#diff-12783128521e452af0cfac94b99b8d250413c516ec71fe6d97dbea666ff7ba27L8-R14)
[[2]](diffhunk://#diff-9917ddc9f1c3304218f7269265b746d997c5c0615478177b5fceecd33ef47cb5R5-R6)
[[3]](diffhunk://#diff-9917ddc9f1c3304218f7269265b746d997c5c0615478177b5fceecd33ef47cb5R126-R129)
[[4]](diffhunk://#diff-dd4fbda47e51f1e35defb9275a9cd9c212ecde0b870cba89ddaaae65c5f3cd28R89-R106)
* Updated `.devcontainer/devcontainer.json` to use the latest Go 1.25.3
version for consistency.

**Licensing and Miscellaneous**

* Added `apps/docs/` to the list of licensed directories in
`LICENSING.md`.

These changes ensure the documentation is now maintained in a modern,
scalable system and all project tooling is updated to support the new
structure.

---------

Co-authored-by: Federico Coppede <[email protected]>

apps/docs/components/docusaurus/doc-card-list.tsx

@@ -0,0 +1,30 @@
+import React from 'react';
+import { Cards, Card } from 'fumadocs-ui/components/card';
+
+export default function DocCardList({ items }: { items?: any[] }) {
+  // If items are provided (manual list), render them
+  if (items) {
+    return (
+      <Cards>
+        {items.map((item, index) => (
+          <Card key={index} href={item.href} title={item.label} />
+        ))}
+      </Cards>
+    );
+  }
+
+  // If no items, it's likely an auto-generated list for the current sidebar category.
+  // Fumadocs doesn't have a direct equivalent to "current sidebar category items" in a component easily accessible here without context.
+  // For now, we'll render a placeholder or nothing to avoid build errors.
+  // In a real migration, we'd use `useTreeContext` or similar if available, or rely on Fumadocs' index page generation.
+  return (
+    <div className="admonition admonition-info alert alert--info">
+      <div className="admonition-heading">
+        <h5>DocCardList Placeholder</h5>
+      </div>
+      <div className="admonition-content">
+        <p>Auto-generated card lists are not yet fully supported in the migration.</p>
+      </div>
+    </div>
+  );
+}