Phase 0: bootstrap Rust workspace

- Cargo workspace with 6 crates: shared, storaged, catalogd, queryd, aibridge, gateway
- shared: types (DatasetId, ObjectRef, SchemaFingerprint, DatasetManifest) + error enum
- gateway: Axum HTTP entrypoint with nested service routers + tracing
- All services expose /health stubs
- justfile with build/test/run recipes
- PRD, phase tracker, and ADR docs

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

justfile

@@ -0,0 +1,28 @@
+# Lakehouse task runner
+
+default:
+    @just --list
+
+# Build all crates
+build:
+    cargo build --workspace
+
+# Run all tests
+test:
+    cargo test --workspace
+
+# Run gateway
+run:
+    cargo run --bin gateway
+
+# Check without building
+check:
+    cargo check --workspace
+
+# Format all code
+fmt:
+    cargo fmt --all
+
+# Lint
+clippy:
+    cargo clippy --workspace -- -D warnings