Replace REST and RabbitMQ with gRPC

Consolidate the two separate communication protocols (protobuf
over REST via Hyper, and RabbitMQ for events) into a single gRPC
interface using tonic. This eliminates the RabbitMQ operational
dependency and gives clients strongly-typed generated stubs.

Events are now delivered via a server-streaming RPC backed by a
tokio broadcast channel. HMAC auth moves to a tonic interceptor
using timestamp-only signing since TLS guarantees body integrity.

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

Author: benthecarman

.github/workflows/e2e-tests.yml

@@ -0,0 +1,23 @@
+name: E2E Tests
+
+on: [ push, pull_request ]
+
+concurrency:
+  group: ${{ github.workflow }}-${{ github.ref }}
+  cancel-in-progress: true
+
+jobs:
+  e2e-tests:
+    runs-on: ubuntu-latest
+    steps:
+      - name: Checkout source code
+        uses: actions/checkout@v6
+      - name: Install Rust stable toolchain
+        run: |
+          curl --proto '=https' --tlsv1.2 -sSf https://sh.rustup.rs | sh -s -- -y --profile=minimal --default-toolchain stable
+      - name: Install protoc
+        run: sudo apt-get install -y protobuf-compiler
+      - name: Run E2E tests
+        run: cd e2e-tests && cargo test
+        env:
+          RUST_LOG: info