feat(market-data): harden bar continuity recovery

[LimiNode]

Summary

• add bounded history retries with owner-loop processing and capped exponential backoff;
• keep live bar batches buffered while history retry is pending;
• add per-route KEEP_ALL / DROP_NON_MONOTONIC bar policy;
• retain the existing FAILED -> LIVE behavior after retry exhaustion;
• update continuity/API documentation, backlog, and the runnable chart-style example;
• cover failed and rejected history requests, retry exhaustion, backoff calculation, and strict timestamp filtering.

This PR is intentionally stacked on feat/market-data-continuity / PR #158.

Verification

• market_data_continuity_test: 16/16;
• market_data_router_test: 21/21;
• market_data_subscription_contract_test: 22/22;
• market_data_continuity_example.cpp: compiled and ran with MinGW.

The full examples configuration is not available in this worktree because the nested tg-client-stdio/external/cpp/tiny-process-library dependency is absent; the continuity example was compiled directly with the same public include/dependency paths.