Address code-review findings: split TransactionService, dead deps, deprecated APIs, exception hygiene

Fix the non-test findings from the quality review:

• Q-001: split TransactionServiceImpl (1051 LOC) into sensible collaborators (partial-fill math, goods transfer, post-trade reactions); trim noisy comments.
• Q-004: remove dead compileOnly deps (ItemBridge, log4j-core, RedProtect) + orphaned repos.
• Q-005: migrate deprecated Bukkit text/item APIs (ChatColor, Sign getLine/setLine, ItemMeta getDisplayName/hasDisplayName, ItemStack getDurability) to Adventure/modern equivalents.
• Q-006: log the swallowed Throwables in MarketListener best-effort hooks.
• Q-007: make the AccountServiceImpl empty ExecutionException catch explicit.
• Q-008: replace settle(..., boolean buy, ...) flag with a Direction enum.
• Q-009: reduce services/impl static reach-back into ChestShop (inject data-folder/paths).
• Q-010: replace vendored Base64 with JDK java.util.Base64 if the custom object-serialization features are dead. Skipped per direction: Q-002 (coverage — intentionally low until rearchitecture done) and the coverage-gate half of Q-003.