fix: add feed listing to SDK clients

[realfishsam]

Summary\n- Add listFeeds()/list_feeds() to the TypeScript and Python FeedClient wrappers\n- Hit GET /api/feeds/ so callers can discover available feed names before constructing a client\n- Add focused unit tests for both SDKs\n\n## Tests\n- python3 importlib smoke check for the Python client\n- TypeScript source-level smoke check for the new listFeeds() path\n- git diff --check\n\nFixes #834

[realfishsam]

PR Review: FAIL

What This Does

Adds feed-listing support to SDK feed clients so consumers can discover available feeds from SDKs.

Blast Radius

Python/TypeScript feed clients, feed-client tests, and API references.
Changed files reviewed: core/api-doc-config.generated.json, sdks/python/API_REFERENCE.md, sdks/python/pmxt/feed_client.py, sdks/python/tests/test_feed_client.py, sdks/typescript/API_REFERENCE.md, sdks/typescript/pmxt/feed-client.ts, sdks/typescript/tests/feed-client.test.ts

Consumer Verification

Before (base branch):
Base branch (origin/main) does not include these changes. I reviewed the diff against the base and did not run full live-exchange before/after reproduction in this daily batch.

After (PR branch):
PR branch build PASS; authenticated local sidecar smoke PASS using POST /api/mock/fetchMarkets with x-pmxt-access-token, response snippet: {"success":true,"data":[{"marketId":"mock-m0","eventId":"mock-event-0","title":"Which party wins the 2026 harborland election?","description":"incididunt magna metus ut cupidatat aliquip dolore quis incididunt id do aenean aenean non dolor dolore tempor pharetra lorem fugiat aenean est voluptate ...

Test Results

• Build: PASS (npm run build --workspace=pmxt-core)
• Unit tests: PASS (npm test --workspace=pmxt-core -- --runInBand)
• Server starts: PASS
• E2E smoke: PASS (POST /api/mock/fetchMarkets; live venue-specific calls were not made)
• Dependency install: skipped (existing workspace deps reused)

Findings

1. Generated/API-doc artifacts changed without an obvious source/generator change; verify these are regenerated outputs, not hand edits. Files: core/api-doc-config.generated.json

PMXT Pipeline Check

• Field propagation (3-layer): N/A
• OpenAPI sync: N/A
• Financial precision: N/A
• Type safety: ISSUE
• Auth safety: N/A

Semver Impact

minor -- bug fix/internal compatibility change unless SDK consumers rely on newly added APIs

Risk

The branch was built, core-tested, and authenticated-smoke-tested through the sidecar. Full live-exchange before/after behavior remains unverified for this daily batch; credentialed venue calls and venue API drift should be treated as residual risk unless covered by tests in this PR.