Update conformance alpha5 and TS RC interop

[leehack]

Summary

• bump official conformance package usage from 0.2.0-alpha.4 to 0.2.0-alpha.5
• remove stale 2026 RC server expected failures now that alpha.5 passes those scenarios
• keep the 2026 RC client json-schema-ref-no-deref fixture gap expected
• record overridden conformance package names in 2026 RC summary artifacts
• re-pin the manual TypeScript 2026 RC interop fixture to pkg.pr.new previews from the merged v2-2026-07-28 branch head (9fdb62e) for both client and server packages
• refresh interop/conformance docs to reflect the current TS preview state

Notes

• Published TypeScript split packages are still only 2.0.0-alpha.2, so this keeps the manual 2026 fixture on a branch preview instead of switching to a published TS alpha.
• TypeScript client -> Dart server passes the expanded 2026 fixture.
• Dart preview client -> TypeScript preview server remains diagnostic-only because the TS stateless tools/list response still omits resultType.

Validation

• dart format --output=none --set-exit-if-changed .
• npm ci in test/interop/ts_2026_rc
• dart analyze
• dart run test/conformance/run_2025_server_conformance.dart --timeout-seconds 90 --output-dir .dart_tool/conformance/pr_alpha5_2025_server
• npx -y @modelcontextprotocol/conformance@0.2.0-alpha.5 client --command "dart run test/conformance/mcp_2026_rc_client.dart" --suite all --spec-version 2025-11-25 --verbose -o .dart_tool/conformance/pr_alpha5_2025_client
• dart run test/conformance/run_2026_rc_server_conformance.dart --timeout-seconds 90 --output-dir .dart_tool/conformance/pr_alpha5_2026_server
• dart run test/conformance/run_2026_rc_client_conformance.dart --timeout-seconds 90 --output-dir .dart_tool/conformance/pr_alpha5_2026_client
• dart run tool/testing/run_ts_2026_rc_interop.dart
• dart test test/docs/markdown_docs_test.dart
• dart test

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 84.91%. Comparing base (d01d081) to head (35a1c49).
⚠️ Report is 1 commits behind head on dev/2026-07-28-rc.

Additional details and impacted files

@@                Coverage Diff                 @@
##           dev/2026-07-28-rc     #289   +/-   ##
==================================================
  Coverage              84.91%   84.91%           
==================================================
  Files                     70       70           
  Lines                  15394    15394           
==================================================
  Hits                   13072    13072           
  Misses                  2322     2322           

Flag	Coverage Δ
cli	76.74% <ø> (ø)
unittests	88.45% <ø> (ø)

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