Add full-content evlog observability

[fmhall]

Summary

• add evlog's Eve hook for full turn and session wide events, with redaction deliberately disabled for debugging
• correlate evlog events with Eve telemetry while recording full model inputs, outputs, and inbound channel request spans
• record Linq reaction accepted, skipped, and failed outcomes without letting detached evlog state interfere with the optional tapback
• keep repeated reaction observations append-only within a turn and out of later turns

Validation

• pnpm exec vitest run tests/agent/channels/linq-message-delivery.test.ts tests/agent/hooks/evlog.test.ts (2 files, 14 tests)
• pnpm check (47 files, 224 tests; lint, types, format, Knip, and boundaries)
• pnpm build
• pnpm build:eve
• git diff --check origin/main...HEAD
• authenticated local pnpm dev smoke: eve invoke returned evlog-final-smoke; the emitted wide event preserved the complete unredacted request markers, message parts, response, token usage, and finish reason

Review notes

• evlog is pinned to 2.27.1 because the repository's 24-hour minimum release age blocked 2.28.0 on August 31.
• Full message/model content and redact: false are intentional for the current debugging phase.
• Linq keeps direct console fallbacks because evlog 2.27.1's turn logger can be detached when durable Eve work resumes in another process.
• The local smoke verified the evlog wide event. The authored instrumentation file did not produce an additional .eve/traces artifact locally without an OpenTelemetry setup; hosted trace export remains provider-owned.