docs: add README, LICENCE, and production config template

- Add MIT LICENCE file
- Add comprehensive README with tech stack, API overview, and architecture docs
- Add example production configuration template
- Remove gradle.properties in favour of build-time version injection
@

config/application-prod.yaml.example

@@ -0,0 +1,55 @@
+spring:
+  datasource:
+    url: jdbc:postgresql://localhost:5432/dfguide_dev
+    username: postgres
+    password: 123456
+    driver-class-name: org.postgresql.Driver
+  data:
+    redis:
+      host: localhost
+      port: 6379
+      database: 0
+      # password: 6hLFVqfGPviTYukn # Uncomment if password is necessary
+
+logging:
+  pattern:
+    # dateformat: dd MMM yyyy HH:mm:ss.SSS # Modify this for custom date format.
+
+app:
+  common:
+    version: 1.3.0.8-dev # Application version, you can change to any version you like, used for communication with frontend.
+  cors:
+    allowed-origins: # Cross-origin allowed origins
+      - "http://localhost:5173" # Dev server for vite.
+      - "http://localhost:4173" # Preview server for vite.
+    allow-credentials: true # Must be set to `true` since we are using cookie. You can change it only when you have modified how this application executing authentication.
+    allow-private-network: false
+    allowed-headers:
+      - "Content-Type"
+      - "Authorization"
+    allowed-methods:
+      - GET
+      - POST
+      - PUT
+      - PATCH
+      - DELETE
+    exposed-headers:
+      - "Content-Type"
+      - "Authorization"
+    max-age: PT2H
+  jwt:
+    issuer: dfguide.local # Issuer host
+    secret: qwertyuiopasdfghjklzxcvbnm123456 # JWT singing secret, a 32-byte long or longer string is recommended
+    valid-time: PT2H # JWT valid duration
+  cookie: # Cookie settings.
+    http-only: true
+    secure: false
+    same-site: lax
+    path: '/'
+    max-age: PT2H
+
+springdoc:
+  api-docs:
+    enabled: true # Set to `false` if you do not need api docs (recommended in production mode).
+  swagger-ui:
+    enabled: true # Set to `false` if you do not need swagger ui (recommended in production mode).