Merge upstream: Proxy browser OTLP traces through the server (#1739)

[aaditagrawal]

What

Cherry-picks upstream commit 04a1ae77 (PR #1739) onto the fork.

Upstream changes

Proxies browser OTLP (OpenTelemetry) traces through the server instead of sending them directly from the browser. Adds:

• clientTracing.ts on the web side to collect and batch browser-side spans
• BrowserTraceCollector service on the server to receive and persist traces
• HTTP endpoint on the server for trace ingestion
• TraceRecord enhancements for browser span handling
• Tests for the new trace proxy pipeline

Conflict resolution

None -- clean cherry-pick with no conflicts (13 files, +1010/-41).

Verification

• bun typecheck passes (all 7 packages)
• bun fmt and bun lint clean
• server.test.ts passes (34 tests), LocalFileTracer.test.ts passes (2 tests)
• client.test.ts passes (3 tests), wsTransport.test.ts passes (8 tests)

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ℹ️ Review info

⚙️ Run configuration

Configuration used: defaults

Review profile: CHILL

Plan: Pro

Run ID: 44ffb9ba-f75a-4d1c-b0b5-31123f6728b0

📥 Commits

Reviewing files that changed from the base of the PR and between 0f789b5 and ab1cb58.

📒 Files selected for processing (13)

• apps/server/src/http.ts
• apps/server/src/observability/Layers/Observability.ts
• apps/server/src/observability/LocalFileTracer.test.ts
• apps/server/src/observability/LocalFileTracer.ts
• apps/server/src/observability/Services/BrowserTraceCollector.ts
• apps/server/src/observability/TraceRecord.ts
• apps/server/src/server.test.ts
• apps/server/src/server.ts
• apps/web/src/observability/clientTracing.ts
• apps/web/src/rpc/client.test.ts
• apps/web/src/rpc/client.ts
• apps/web/src/wsTransport.test.ts
• apps/web/src/wsTransport.ts

✨ Finishing Touches

🧪 Generate unit tests (beta)

• Create PR with unit tests
• Commit unit tests in branch merge/upstream-1739-otlp-trace-proxy

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