fix(security) : replace real secrets in .env with placeholders and create .env.example

Secrets moved to .env.local (gitignored). Added .env.example for new developers.
Also added .idea/ and docker/.env.docker.local to .gitignore and removed them from tracking.

Tickets: T-001, T-013, T-018

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

.env

@@ -1,5 +1,5 @@
 APP_ENV=dev
-APP_SECRET="a64f5614357bf56aecb1d7470e431535"
+APP_SECRET="change_me_in_env_local"
 APP_DEBUG=1
 
 DEFAULT_URI=http://localhost/
@@ -11,7 +11,7 @@ CORS_ALLOW_ORIGIN='^https?://(localhost|127.0.0.1)(:[0-9]+)?$'
 ###> lexik/jwt-authentication-bundle ###
 JWT_SECRET_KEY=%kernel.project_dir%/config/jwt/private.pem
 JWT_PUBLIC_KEY=%kernel.project_dir%/config/jwt/public.pem
-JWT_PASSPHRASE=c2dbeec8fa8255bdab24e88b9fc1e57927740c429ae3b930d03e51b92e13a85f
+JWT_PASSPHRASE=change_me_in_env_local
 JWT_COOKIE_SECURE=0
 JWT_TOKEN_TTL=86400
 JWT_COOKIE_TTL=86400
@@ -20,4 +20,4 @@ JWT_COOKIE_TTL=86400
 
 DATABASE_URL="postgresql://${POSTGRES_USER}:${POSTGRES_PASSWORD}@db:${POSTGRES_PORT}/${POSTGRES_DB}?serverVersion=16&charset=utf8"
 
-ENCRYPTION_KEY=aaaaaaaaa
+ENCRYPTION_KEY=change_me_in_env_local