Vendor missing OTLP logs protos and unbreak fresh clones

[jianbo27]

Summary

Fresh clones of `main` cannot start the server. `bun run src/server.ts` fails immediately with:

```
ENOENT: no such file or directory,
open '.../src/proto/opentelemetry/proto/collector/logs/v1/logs_service.proto'
```

`src/protobuf.ts` and `src/grpc.ts` both load `opentelemetry/proto/collector/logs/v1/logs_service.proto` at startup, but neither that file nor `opentelemetry/proto/logs/v1/logs.proto` exists in the repo.

Root cause

`.gitignore` line 14 was an unanchored `logs` pattern intended to ignore a top-level `logs/` directory. Because git patterns without a leading slash match at any depth, this also matched `src/proto/opentelemetry/proto/logs/` and `src/proto/opentelemetry/proto/collector/logs/`, so the vendored `logs.proto` and `logs_service.proto` never made it into the index.

```
$ git check-ignore -v src/proto/opentelemetry/proto/logs/v1/logs.proto
.gitignore:14:logs src/proto/opentelemetry/proto/logs/v1/logs.proto
```

Fix

• Anchor the rule to the repo root: `logs` → `/logs`. Inline comment explains why so this doesn't regress.
• Vendor the two missing `.proto` files from OpenTelemetry's `opentelemetry-proto` v1.8.0. Sha-confirmed all eight vendored protos in this tree (the existing six + these two) are byte-identical to OTel v1.8.0, so the tree is internally consistent. Apache-2.0 license, matching the existing `src/proto/LICENSE`.

Verification

End-to-end on a fresh clone:

• `bun install && bun run src/server.ts` → starts on `0.0.0.0:4318` (HTTP) + `0.0.0.0:4317` (gRPC) without ENOENT.
• `POST /v1/traces` (HTTP/JSON) → HTTP 200, span lands in `data/traces.ndjson`.
• `POST /v1/logs` (HTTP/JSON) → HTTP 200, log record lands in `data/logs.ndjson`.
• `POST /v1/metrics` (HTTP/JSON) → HTTP 200.
• HTTP/protobuf trace from `OTel-OTLP-Exporter-Python/1.41.1` → HTTP 200, decoded payload includes correct `service.name` and span name.
• Real producer end-to-end test: an OpenAI Agents SDK agent on AppWorld emitted 19 spans across 3 traces, all received and decoded correctly; `task compact:traces` produced a valid `traces-by-trace.jsonl`.

`git check-ignore` no longer matches the vendored proto files.