conformance: flux interface spec uses wrong endpoint and architecture

[lukeocodes]

Problem

The flux interface conformance spec (interfaces/flux/conformance/stream.spec.js) fails all 8 tests with 404 errors.

Root Cause

This is a known spec bug affecting all flux starters (node, bun, cpp, csharp):

1. Spec hardcodes /flux/stream endpoint instead of using process.env.FLUX_ENDPOINT || "/api/flux"
2. Spec assumes stream_url ingestion architecture, but all starters use WebSocket proxy architecture

Test Results

• API tests (tests/flux/api/): 5 passed (metadata + stream proxy tests)
• UI tests: 2 passed
• Interface conformance: 0/8 (known spec architecture mismatch)

Note

Same issue as node-flux#1, bun-flux#1, cpp-flux#1. Fix needed in the shared contracts/spec, not in individual starters.