feat: docs v2 (#2460)

Co-authored-by: Catalin Pit <catalinpit@gmail.com>

apps/docs/content/docs/concepts/index.mdx

@@ -0,0 +1,70 @@
+---
+title: Concepts
+description: Foundational concepts behind document signing, recipient roles, field types, and certificates.
+---
+
+## Core Concepts
+
+<Cards>
+  <Card
+    title="Document Lifecycle"
+    description="How documents move from draft to pending to completed or rejected."
+    href="/docs/concepts/document-lifecycle"
+  />
+  <Card
+    title="Recipient Roles"
+    description="Signers, approvers, viewers, assistants, and CC recipients."
+    href="/docs/concepts/recipient-roles"
+  />
+  <Card
+    title="Field Types"
+    description="Signatures, text, dates, checkboxes, dropdowns, and more."
+    href="/docs/concepts/field-types"
+  />
+  <Card
+    title="Signing Workflow"
+    description="The complete process from preparing a document to collecting signatures and sealing the final PDF."
+    href="/docs/concepts/signing-workflow"
+  />
+  <Card
+    title="Signing Certificates"
+    description="How documents are digitally signed and verified."
+    href="/docs/concepts/signing-certificates"
+  />
+</Cards>
+
+---
+
+## How These Concepts Apply
+
+These concepts work consistently across all ways you interact with Documenso:
+
+- **Web application**: When you create documents in the UI, you'll select recipient roles, add fields, and track documents through their lifecycle states.
+
+- **API integration**: The same concepts map directly to API endpoints. Documents have status fields, recipients have role properties, and fields have type configurations.
+
+- **Self-hosting**: The signing certificate concept becomes particularly relevant when you deploy your own instance and configure your own certificates for document signing.
+
+Understanding these fundamentals will make the rest of the documentation easier to follow.
+
+---
+
+## Related Sections
+
+<Cards>
+  <Card
+    title="User Guide"
+    description="Apply these concepts when sending documents."
+    href="/docs/users"
+  />
+  <Card
+    title="Developer Guide"
+    description="Work with these concepts through the API."
+    href="/docs/developers"
+  />
+  <Card
+    title="Compliance"
+    description="How these concepts relate to legal standards."
+    href="/docs/compliance"
+  />
+</Cards>