docs: update password generation to use hex encoding

Change openssl rand commands from base64 to hex encoding to avoid
special characters that break URL parsing in database connection strings.

- JWT_SECRET: openssl rand -hex 32
- DBPASS: openssl rand -hex 16

Updated in:
- .env.example
- README.md
- docs/contributing/DEVELOPMENT.md
- docs/operations/troubleshooting.md

README.md

@@ -29,7 +29,10 @@ cd bookhoard
 
 # 2. Set up environment
 cp .env.example .env
-# Edit .env with your secure JWT_SECRET and DBPASS
+# Generate secure passwords (no special characters):
+#   JWT_SECRET: openssl rand -hex 32
+#   DBPASS: openssl rand -hex 16
+# Edit .env with your generated values
 
 # 3. Start the server
 podman-compose up --build -d  # or: docker-compose up --build -d