fix(analytics): store bounded product-usage rollup dimensions complete

[galuis116]

Closes #383.

Summary

buildProductUsageDailyRollupRecord stored every dimension via countProductUsageDimensions, which keeps only the top 20 by frequency. That is correct for the unbounded byRepo / byCommand / byTool / byRouteClass dimensions (shown as display top-N), but byEvent is a bounded event-name enum (~22 distinct names) that the weekly value report consumes by exact-name lookup (sumEvent -> byEvent.find(eventName)). On a day with more than 20 distinct event types, the lowest-frequency events drop off the cut — and the report's flagship signals (agent_pr_packet_completed, agent_preflight_branch_completed, agent_command_replied/skipped) are exactly the low-frequency ones, so the public weekly value report under-counts them (reads 0 for that day).

Scope

• src/db/repositories.ts — store the bounded enum dimensions (bySurface / byOutcome / byEvent) complete via a FULL_DIMENSION_LIMIT, while the genuinely-unbounded byRepo / byCommand / byTool / byRouteClass keep their display top-N. A comment marks the bounded-vs-unbounded distinction so the two classes can't be conflated again.
• test/unit/product-usage.test.ts — high-diversity-day test.

No schema, API, or public-surface changes (the rollup record shape is unchanged; only the bounded dimensions are no longer truncated).

Validation

npx vitest run test/unit/product-usage.test.ts test/unit/weekly-value-report.test.ts \
  test/unit/operator-dashboard.test.ts test/unit/product-usage-mcp-adoption.test.ts   # 29/29
npx vitest run test/integration/api.test.ts test/unit/queue.test.ts                   # 58/58
npx tsc --noEmit                                                                      # clean
git diff --check                                                                      # clean (no whitespace errors)

Branch coverage stays >= 97%. CI validate is green.

Safety

• Privacy-safe: byEvent holds bounded, sanitized event names (already redacted/normalized at record time) and small per-day counts — storing the complete bounded enum adds no actor/repo PII and only marginally more rows (bounded by the enum size).
• The unbounded repo/command/tool/route dimensions are unchanged, so there is no unbounded growth in the stored rollup.

Notes

• The weekly value report is a public + operator trust artifact persisted to an audit event, so the undercount directly understated miner-utility / maintainer-value headline metrics on the busiest days.
• Reachable when a single UTC day has > 20 distinct event types (active days mixing agent/auth/mcp/github events).