fix(company): scope company page stats to PRs credited to the company

[PrestaEdit]

Problem

On company pages (e.g. /company/wepika):

1. "0 contributors" while one contributor is listed: employees is usually an empty array, and [].length ?? contributors.length never falls back.
2. Stats belong to the members, not the company. aggregateContributors summed each member's lifetime stats, on the assumption that they matched the company's counters. They don't: Traces attributes each PR separately (sponsor company, else employee time frame). Wepika showed 492 merged PRs / 236 reviews, but only 3 PRs are attributed to it. 71 of 83 companies were inflated (Kiwik: 36 → 1325, AGRO-LA: 1 → 974…).

Fix

• The page builds its view from the company object itself (merged_pull_requests(_by_year)), and aggregateContributors is removed.
• Reviews, issues, opened PRs, merge rate and the PR breakdown donut are hidden on company pages: they have no sponsor company, so Traces cannot attribute them. The yearly chart and the year drilldown drop series that have no data.
• New companyMembers() helper (employees if non-empty, else PR-derived contributors), used for the subtitle and the Contributors KPI.
• Repository sections read the new per-company repositories / repositories_by_year from feat(topcompanies): emit merged PRs per repository for each company traces#254. They stay hidden until that data is published, so this PR can be merged first.

Verification

• New unit tests in useEntityDetail.spec.ts: company counters, repos present or absent, companyMembers fallback. The full suite (61 tests) and eslint pass.
• Checked in the browser: Wepika and Kiwik now show only the PRs attributed to them, with the right contributor count. With JSON generated by traces#254, Top repositories / All repos come back with per-company numbers. The contributor page is unchanged.

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