[109] ISSUE-082: Add Soroban Transaction Time Bounds Example

[esthertitilayo-dev]

Summary

• Adds src/examples/82-transaction-time-bounds.ts: connects to Soroban RPC, computes/validates a time-bounds window, simulates/signs/submits a contract invocation within it, then deliberately builds an already-expired window (no real-time wait) to demonstrate rejection, and a deliberately invalid config to demonstrate graceful validation. Exports pure, network-free helpers (computeTimeBounds, validateTimeBounds, isExpired, isNotYetValid, describeValidityWindow, explainTimeBoundsFailure) for unit testing.
• Adds tests/transaction-time-bounds.test.ts covering all the pure helpers plus runner/README registration.
• Registers 82-transaction-time-bounds in src/runner/catalog.ts and documents it in README.md (roadmap list + Direct Run section).
• Adds a validation.config.json exclusion for the new live-network example.
• Also fixes a pre-existing JSON syntax bug in src/validation/validation.config.json (the 67-soroban-contract-events exclusion entry was missing its closing }, and the next entry's opening {, which broke JSON parsing for the whole config).

Closes #109

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