docs(telemetry): document semconv v1.43 schema URL compatibility

[Sayt-0]

Summary

• Document the resource and instrumentation-scope schema_url values emitted after the OpenTelemetry SDK 1.45 migration.
• Explain compatibility for pass-through consumers and migration requirements for schema-validating or translating pipelines.
• Add an OTLP/HTTP regression test that verifies the semconv v1.43 resource schema URL in the serialized trace payload.

Issue requirements

Requirement	Implementation
Verify emitted schema_url behavior	The regression test decodes a real OTLP trace request and checks the resource and scope schema URLs.
Verify consumed schema_url behavior	Documentation distinguishes pass-through ingestion from schema-aware validation and translation.
Document compatibility and migration guidance	The OpenTelemetry guide covers the move from resource schema 1.41.0 to 1.43.0, independent scope schemas, and allowlist/translator updates.
Prevent unintended changes	Literal resource and wire-level assertions pin https://opentelemetry.io/schemas/1.43.0.

Validation

• task test
• task build
• go test ./cmd/root/... -run '^TestTraceExportEmitsResourceSchemaURL$' -race -count=10
• go vet ./cmd/root/...
• go build ./...
• go mod tidy -diff
• npx --yes markdownlint-cli2@0.22.1
• ./scripts/docs-check-canonical.sh
• ./scripts/docs-check-llms-txt.sh
• git diff --check

task docs-check-links remains blocked by unrelated existing external 403/404 responses and a pre-existing missing MCP documentation anchor. The installed golangci-lint was built with Go 1.26 and cannot lint a repository targeting Go 1.27.

Closes #4047