fix: Enforce strict tier-based access control for node endpoints

Access control hierarchy:
- Anonymous (free): db-sync read-only ONLY, no node access
- Standard (≥50 TRP): db-sync + node read (UTxOs, protocol-params)
- Elevated (≥500 TRP): everything + tx submit
- Master: unrestricted

Node endpoints now return HTTP 403 for insufficient tier:
- GET /v1/address/{addr}/utxos → requires standard+
- GET /v1/protocol-params → requires standard+
- POST /v1/tx/submit → requires elevated+ (403 for standard/anonymous)

Added require_standard_tier and require_elevated_tier dependencies.

Dockerfile

@@ -5,7 +5,6 @@ RUN apt-get update && apt-get install -y --no-install-recommends \
     curl \
     ca-certificates \
     libsodium23 \
-    libsecp256k1-1 \
     libnuma1 \
     && rm -rf /var/lib/apt/lists/*