feat(schema): update to v1.25.0 and v2.0.0-alpha.8

[benbrandt]

Summary

• Update the v1 schema release to 1.25.0 and the draft v2 release to 2.0.0-alpha.8; regenerate schema types, validators, and guards.
• Expose the new IdleStateUpdate extensible-union guards, including the error and omitted/null stop-reason variants, and update the active-session stop-reason type.
• Normalize schema-marked malformed optional stop-reason tags before union selection, preserving valid known/custom tags and strict known-payload validation.
• Validate original optional referenced payloads in narrowing guards so malformed raw error details are not narrowed to valid errors; wire parsing retains its declared lenient behavior.
• Reflect stabilized session notices and compaction in generated API descriptions and keep TypeDoc alias configuration aligned with the new exports.

Validation

• npm run generate
• npm run check: generation consistency, lint, formatting, spellcheck, build, 976 tests, and TypeDoc verification
• Targeted runtime checks for malformed/omitted/null stop reasons, error details and guards, custom payload preservation, and strict known updates/MCP server entries
• git diff --check

No new tests or handwritten documentation were added, per repository instructions. Request arrays follow the published JSON schemas, including intentional rejection of null; no null-default workaround was added.