Preserve configured OpenTelemetry resource attributes across all signal pipelines

Description

Audit dimension 3 confirmed a live configuration defect at the v2.0.0 release tree. src/meraki_dashboard_exporter/core/config_models.py:681-684 promises additional OpenTelemetry resource attributes, but core/otel_tracing.py:62-69 constructs a resource from four exporter-owned keys and consults the configured mapping only for the legacy environment key. The same builder feeds traces at otel_tracing.py:174, data logs at core/otel_data_logs.py:219, and bridged metrics at core/otel_metrics.py:555. Configuring a nonstandard attribute such as cloud.region or service.namespace therefore silently drops it from every signal, including target_info. Tests use an empty mapping or compare consumers against the same faulty builder, so they do not cover the promised behavior.

Acceptance Criteria

• #1 Every configured OpenTelemetry resource attribute is preserved identically in trace, data-log and metrics-bridge resources
• #2 Exporter-owned service.name, service.version and service.instance.id values remain authoritative when configured attributes collide
• #3 The documented environment compatibility mapping remains supported and is covered alongside a nonstandard attribute

Definition of Done

• #1 just check (ruff format –check, ruff check, mypy, generated-doc drift, offline API conformance, and the marker-filtered pytest run with the 80% coverage floor — this is exactly what the CI test job runs)
• #2 just gen, when metrics, config, endpoints, collectors, the settings schema or the chart config changed — just check includes the drift gate and CI fails the build on it
• #3 Grafana queries in grafana/dashboards/*.json and grafana/alerts/ updated, if a metric or label name changed

Implementation Plan

1. Add a failing resource-builder regression with a nonstandard configured attribute, legacy environment mapping and collisions against exporter-owned identity keys. 2. Merge configured attributes before applying exporter-owned identity fields and the resolved deployment environment. 3. Prove trace, data-log and metrics consumers all receive the same resource through focused tests, then return the uncommitted diff to root.

Implementation Notes

Test-first evidence: the configured nonstandard resource-attribute regression failed before the source change with a missing cloud.region attribute. The implementation merges configured attributes first, translates legacy environment, and then applies authoritative exporter identity fields. Focused cross-signal tests passed, the owned modules passed 70 tests, integrated just check passed 2,939 tests with 5 deselected at 91.25% coverage, and just ci passed all Docker legs. No metric or label name changed.

Final Summary

Implemented in 822c6f4: configured OpenTelemetry resource attributes now survive identically into tracing, data logs and bridged metrics while exporter-owned service identity remains authoritative. Verified across all three signal paths and the complete local gates.