Fix coherent find-text-notes capability schema

[epowell40]

Summary

• publish one explicit native schema for optional find-text-notes selectors before the net48 reflection fallback
• align the typed MCP tool with the certified native contract
• retain fail-closed type and bound validation and regenerate certified trust artifacts

Causal boundary

Candidate 11 reached truthful clarification and then failed before dispatch because net48 reflection advertised nullable string selectors as jointly required. The handler and native validator already treated them as optional; this repair fixes the producer contract rather than weakening the consumer validator.

Validation

• failing-before native producer regression reproduced the incorrect fallback
• MCP focused regressions: 13/13
• MCP complete compiled test suite: green
• RevitBridge.Common.Tests net8: 837/837
• RevitBridge.Common.Tests net48: 837/837
• operator-backend full suite: 2,891 passed, 3 skipped, 0 failed
• converged L0-L2 source certification: green
• repository, architecture, module-size, exposure-policy, and certification checks: green