Remove telemetry: usage metrics and OTel command spans

[sorcerai]

Summary

Removes all telemetry from bd: the anonymous usage-metrics pipeline (internal/metrics + dolthub/eventkit, per-command cli_command events, the $HOME/.beads/eventsData queue, the detached bd send-metrics uploader posting to gastownhall-eventsapi.com) and the OpenTelemetry command-span wiring (command_telemetry.go, initTelemetry/startCommandSpan, the telemetry-only argv scrubbers).

What changed

• Deleted internal/metrics/ (event queue, flusher, spawn, machine-id, user-config), cmd/bd/metrics.go, cmd/bd/send_metrics.go, cmd/bd/command_telemetry.go, cmd/bd/telemetry_redact.go, and their tests.
• Unwired cmd/bd/main.go: usage-metrics bootstrap, send-metrics handling, metrics no-DB command entry, first-run notice, CloseAndFlush, OTel init/span/shutdown, commandSpan state, secretFlagTokens/scrubArgsForTelemetry and the DSN-scrub family (telemetry-only).
• Config: removed metrics.disabled / metrics.endpoint defaults and the MetricsDisabledByUserConfig / UserMetricsEndpoint / MetricsNoticeShownByUserConfig plumbing; metrics. dropped from recognized prefixes. User-global mechanism itself kept (node_id still uses it).
• Tests: removed BD_DISABLE_METRICS / BD_DISABLE_EVENT_FLUSH / DO_NOT_TRACK harness vars (now dead); rewrote the user-global provenance/authority tests around node_id; kept the no-telemetry-residue guards (eventsData must not appear under isolated HOME).
• Docs: deleted docs/cli-reference/metrics.md and docs/reference/observability.md; removed bd metrics from CLI_REFERENCE.md, cli-reference index, and docs nav.
• go.mod: github.com/dolthub/eventkit removed via go mod tidy.

Notes for reviewers

• internal/telemetry/ (instrumented storage decorators) is intentionally kept: telemetry.Init now has zero callers, so it is permanently no-op, and the decorators are load-bearing types for the storage chain. BD_OTEL_ENABLED no longer activates anything.
• cmd/bd/doctor/perf_dolt.go's local DoltPerfMetrics variable is unrelated performance reporting, untouched.
• Net diff: 194 files, −6785/+119 — overwhelmingly deletions of instrumentation blocks.

Validation

• go build ./... — clean
• go vet ./... — clean
• Targeted unit tests pass: internal/config user-global authority tests, cmd/bd config-show provenance test, storage-decorator wiring tests
• Full integration suite not run (per task scope)