Phase 5: hardening — gRPC, observability, auth, config

- proto: lakehouse.proto with CatalogService, QueryService, StorageService, AiService
- proto crate: tonic-build codegen from proto definitions
- catalogd: gRPC CatalogService implementation
- gateway: dual HTTP (:3100) + gRPC (:3101) servers
- gateway: OpenTelemetry tracing with stdout exporter
- gateway: API key auth middleware (toggleable)
- shared: TOML config system with typed structs and defaults
- lakehouse.toml config file
- ADR-006 and ADR-007 documented

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

data/_catalog/manifests/4828e537-2524-4af1-9acb-ed075d11e7ee.json

@@ -1,15 +0,0 @@
-{
-  "id": "4828e537-2524-4af1-9acb-ed075d11e7ee",
-  "name": "events",
-  "schema_fingerprint": "test",
-  "objects": [
-    {
-      "bucket": "data",
-      "key": "datasets/events.parquet",
-      "size_bytes": 800,
-      "created_at": "2026-03-27T11:18:02.318643343Z"
-    }
-  ],
-  "created_at": "2026-03-27T11:18:02.318648066Z",
-  "updated_at": "2026-03-27T11:18:02.318648066Z"
-}

data/_catalog/manifests/f4c0f89b-85bf-4af6-8692-8e1cc81c357a.json

@@ -1,15 +0,0 @@
-{
-  "id": "f4c0f89b-85bf-4af6-8692-8e1cc81c357a",
-  "name": "scores",
-  "schema_fingerprint": "test",
-  "objects": [
-    {
-      "bucket": "data",
-      "key": "datasets/scores.parquet",
-      "size_bytes": 800,
-      "created_at": "2026-03-27T11:18:02.317035729Z"
-    }
-  ],
-  "created_at": "2026-03-27T11:18:02.317042772Z",
-  "updated_at": "2026-03-27T11:18:02.317042772Z"
-}