chore(cleanup): R-b R1 — Voyage's own stats, events and OTel export removed

Removes Voyage's measurement, statistics and export apparatus (decision 189;
condition 175 met in step 1) and the R-a leftovers: lib/stats/, lib/exporters/,
the otel-export and post-bash-stats hooks, yardstick, end-state and comparison
gates, synthesis-measure, gold-scorer, docs/observability.md,
examples/observability/, docs/T1-cc26-delegated-orchestration.md and their
tests and fixtures. The six command stats phases and the /trekexecute
main-merge event blocks go; intent-approval --stamp no longer emits
brief-approved. README and docs point to Claude Code's own OpenTelemetry.

Files removed: 52. Files edited: 37.
npm test: 2930 tests (2928 pass / 0 fail / 2 skipped) before, 2600 tests
(2598 pass / 0 fail / 2 skipped) after. removed-surfaces group R1 green.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

docs/profiles.md

@@ -229,7 +229,6 @@ numbers after ≥ 3 runs of each profile.
 
 - [`README.md` § Profile system](../README.md) — top-level overview
 - [`CLAUDE.md` § Profile system](../CLAUDE.md) — internal reference
-- [`docs/observability.md`](observability.md) — JSONL → OTel pipeline
 - [`tests/synthetic/profile-jaccard-calibration.md`](../tests/synthetic/profile-jaccard-calibration.md)
   — calibration status and threshold rationale
 - [`lib/profiles/`](../lib/profiles/) — built-in profile YAMLs