chore: simplify docs structure

docs/openapi.yaml

@@ -1,7 +1,16 @@
-openapi: 3.1.0
+openapi: 3.0.3
 info:
   title: Bit - URL Shortener API
-  description: A high-performance URL shortener service with click tracking and analytics
+  description: |
+    Fast, lightweight, self-hosted URL shortener service with minimal click tracking.
+
+    ## Getting Started
+
+    For setup instructions, please check the [README](https://github.com/sjdonado/bit/blob/master/README.md).
+
+    ## Authentication
+    
+    Multiple users are supported via `X-Api-Key` headers. Create, list and delete keys via the [CLI](https://github.com/sjdonado/bit/blob/master/SETUP.md#cli).
   version: 1.0.0
   contact:
     name: API Support
@@ -423,24 +432,24 @@ components:
           example: Mozilla/5.0 (Macintosh; Intel Mac OS X 10.15; rv:127.0) Gecko/20100101 Firefox/127.0
         country:
           type: string
-          nullable: true
           description: Country code (ISO 3166-1 alpha-2)
           example: US
+          nullable: true
         browser:
           type: string
-          nullable: true
           description: Browser name
           example: Firefox
+          nullable: true
         os:
           type: string
-          nullable: true
           description: Operating system
           example: Mac OS X
+          nullable: true
         referer:
           type: string
-          nullable: true
           description: Referer domain or utm_source
           example: Direct
+          nullable: true
         created_at:
           type: string
           format: date-time
@@ -457,9 +466,9 @@ components:
         next:
           type: integer
           format: int64
-          nullable: true
           description: Cursor for next page (link/click ID)
           example: 12
+          nullable: true
 
     Error:
       type: object