♻️ Deduplicate log primitives and MCP tool result boilerplate

[renardeinside]

Summary

• Move shared log primitives (LogAggregator, AggregatedRecord, should_skip_log, get_aggregation_key, source_label) to apx-common so both CLI and MCP use the same code
• Add effective_timestamp_ms() and source_label() methods on LogRecord, replacing 6 inline timestamp fallback calculations and 3 duplicated service-name mappings
• Change LogAggregator to return structured AggregatedRecord instead of pre-formatted strings, eliminating parse_formatted_log_line() round-trip
• Extract query_filtered_logs() helper to deduplicate setup between fetch_logs and fetch_logs_structured
• Add ToolResult::from_serializable() and structured_error(), replacing 6 identical serialize-or-error patterns in MCP server
• Remove duplicate RefreshOpenapiArgs (identical to EmptyArgs)

Test plan

• cargo test --workspace — all 151 tests pass
• just fmt — no formatting issues
• just check — cargo check, clippy, ruff, prettier all pass

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