feat: add configurable telemetry support

[markovejnovic]

Summary

• Add [telemetry] config block with vendor (bool, default false) and collector-url (optional string) for configuring OpenTelemetry trace export
• Make OTLP dependencies always-included (remove __otlp_export feature flag) so telemetry is runtime-configurable
• Refactor Trc tracing builder to accept telemetry config and create per-endpoint OTLP batch exporters
• Reorder main.rs to load config before tracing init so telemetry settings are available
• Add vendor telemetry opt-in prompt to onboarding wizard (default: yes)

Resolves MES-717

Config example

[telemetry]
vendor = true
collector-url = "https://my-collector.example.com"

Both vendor and collector-url can be active simultaneously — each gets its own independent OTLP batch exporter.

Remaining work

Grafana Alloy deployment at telemetry.priv.mesa.dev is tracked separately as infrastructure work.

Test plan

• 7 new unit tests for TelemetryConfig deserialization and endpoints() logic
• cargo clippy --all-targets --all-features -- -D warnings passes
• All 50 tests pass
• Manual: run onboarding wizard, verify telemetry prompt appears after org setup
• Manual: set vendor = true in config, verify OTLP exporter initializes (check "Telemetry export enabled" log)

[mesa-dot-dev]

Mesa Description

Summary

• Add [telemetry] config block with vendor (bool, default false) and collector-url (optional string) for configuring OpenTelemetry trace export
• Make OTLP dependencies always-included (remove __otlp_export feature flag) so telemetry is runtime-configurable
• Refactor Trc tracing builder to accept telemetry config and create per-endpoint OTLP batch exporters
• Reorder main.rs to load config before tracing init so telemetry settings are available
• Add vendor telemetry opt-in prompt to onboarding wizard (default: yes)

Resolves MES-717

Config example

[telemetry]
vendor = true
collector-url = "https://my-collector.example.com"

Both vendor and collector-url can be active simultaneously — each gets its own independent OTLP batch exporter.

Remaining work

Grafana Alloy deployment at telemetry.priv.mesa.dev is tracked separately as infrastructure work.

Test plan

• 7 new unit tests for TelemetryConfig deserialization and endpoints() logic
• cargo clippy --all-targets --all-features -- -D warnings passes
• All 50 tests pass
• Manual: run onboarding wizard, verify telemetry prompt appears after org setup
• Manual: set vendor = true in config, verify OTLP exporter initializes (check "Telemetry export enabled" log)

^{Description generated by Mesa. Update settings}

[markovejnovic]

LGTM, but needs testing

[mesa-dot-dev]

Performed full review of 0453e34...491ab6d

Analysis

1. Telemetry initialization happens up front for every execution path, which could impact performance in paths that don't need tracing capabilities.

2. The exporter lifecycle is tightly coupled to process lifecycle (initialization, daemonization, shutdown), which may create issues with fork-safety and accurate success reporting.

3. Early failures before config loading fall back to eprintln!, creating inconsistent command-line user experience depending on whether tracing was initialized.

4. System correctness now depends on config validation and process lifecycle management rather than cargo features, introducing new potential points of failure.

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