fix: Docker support, WAL race condition, pusher panic fixes

- Add multi-stage Dockerfile with tini, non-root user, healthcheck
- Fix SQLite WAL mode race between bal-server and bal-pusher (busy_timeout + retry)
- Fix tbl_stats missing UNIQUE index for ON CONFLICT clause
- Replace unwrap() panics in bal-pusher with graceful error handling
- Add docker/entrypoint.sh with BAL_PUSHER_NETWORK support
- cargo fmt across all files

.dockerignore

@@ -0,0 +1,58 @@
+# Git
+.git
+.gitignore
+.gitsecret
+
+# Build artifacts
+target/
+
+# Environment files (secrets)
+*.env
+.env
+.env.*
+!.env.example
+
+# Private keys
+*.pem
+*.key
+!public_key.pem
+!data/public_key.pem
+
+# Database files
+*.db
+*.db-shm
+*.db-wal
+
+# Documentation
+docs/
+*.md
+!README.md
+
+# Tests
+tests/
+
+# Scripts (local dev only)
+bal-server.sh
+bal-pusher.sh
+download_bal_db.sh
+sendtx.sh
+lib.sh
+contrib/
+update
+update_codebase.txt
+
+# Service files
+*.service
+
+# IDE
+*.swp
+*.swo
+.vscode/
+.idea/
+
+# Misc
+Cargo.lock
+generate_random_ascii.sh
+test/
+invalid_txs/
+valid_txs/