docker: add release Dockerfile, fix build deps and feature-split builds

- Add Dockerfile.release: downloads latest release from Gitea, verifies SHA-256
- Fix Dockerfile: remove unused libsodium/cmake, add libsqlite3-dev
- Split build per binary with --no-default-features --features server/pusher
- Remove Cargo.lock from .dockerignore for reproducible builds
- Update README and knowledge base with Dockerfile.release docs

.dockerignore

@@ -16,7 +16,6 @@ target/
 *.pem
 *.key
 !public_key.pem
-!data/public_key.pem
 
 # Database files
 *.db
@@ -51,7 +50,6 @@ update_codebase.txt
 .idea/
 
 # Misc
-Cargo.lock
 generate_random_ascii.sh
 test/
 invalid_txs/