Add CLI tracing proxy exporter

[phinze]

Summary

• CLI deploy spans now ship through the server's existing RPC connection automatically — no OTEL_EXPORTER_OTLP_ENDPOINT needed on the client side
• New Telemetry.reportSpans(bytes) RPC endpoint receives serialized OTLP protobuf and forwards it to the server's configured collector
• Server silently drops spans when no collector is configured; RPC errors are swallowed so tracing never blocks deploys

Design

Three layers, all simple:

Layer	File(s)	What it does
Proxy client	pkg/otelproxy/proxy.go	Implements otlptrace.Client, marshals spans to protobuf, sends via RPC
RPC endpoint	api/telemetry/ + servers/telemetry/server.go	Receives bytes, HTTP POSTs to {OTEL_EXPORTER_OTLP_ENDPOINT}/v1/traces
CLI integration	cli/commands/deploy.go	Connects to telemetry service, sets up proxy tracing. Falls back to no-op if server unreachable

The proxy client lives in pkg/otelproxy/ (not pkg/rpc/) to avoid an import cycle through the generated telemetry RPC code.

Test plan

• go generate ./api/telemetry/... succeeds
• make bin/miren builds clean
• make lint passes (0 issues)
• make test passes (3287 tests, 20 pre-existing skips)
• Manual: start dev server with OTEL_EXPORTER_OTLP_ENDPOINT pointed at a collector, run m deploy without any env vars on the CLI side, verify deploy+build spans appear in the collector

[coderabbitai]

📝 Walkthrough

Walkthrough

This pull request introduces a server-assisted distributed tracing architecture. New IDL and generated RPC bindings define a Telemetry interface with a reportSpans method. A new telemetry server implementation reads OTLP configuration from environment variables and forwards span data to a remote OTLP endpoint. An RPC proxy client enables CLI commands to export traces through this server instead of directly. The telemetry service is integrated into the coordinator and exposed over RPC at path dev.miren.runtime/telemetry. Dependencies for OTLP modules are updated, and the deploy command now uses the proxy-based tracing setup.

---

No actionable comments were generated in the recent review. 🎉

---

_{Comment @coderabbitai help to get the list of available commands and usage tips.}

[evanphx]