fix(scans): show hostname/IP on scan detail header, not a raw UUID

[remyluslosius]

The Scan detail page (/scans/{id}) Host field rendered
scan.host_id.slice(0, 8) — a truncated UUID (e.g. 019eccd8) that isn't
human-friendly. Per request: show the hostname if present, else the IP
address (short UUID only as an impossible-case last resort).

Changes

Backend (api-scans v1.1.0 — C-07 / AC-08)

• GET /scans/{id} resolves the host's hostname + ip_address from the
  hosts table onto ScanSummary, using host(ip_address) for clean
  inet→text and COALESCE for NULLs. A missing host row (FK is
  ON DELETE RESTRICT, so unexpected) leaves the labels empty rather than
  failing the read. The list endpoint (GET /scans) omits them — the caller
  already has host context.

Frontend (frontend-scan-detail v1.1.0 — C-08 / AC-08)

• The Host field renders scan.hostname || scan.ip_address || scan.host_id.slice(0, 8),
  still wrapped in the /hosts/$hostId Link.

Tests

• Backend AC-08: GET /scans/{id} returns the hostname + IP for a named
  host; an empty-hostname host yields empty hostname + populated IP.
• Frontend AC-08: source-inspection of the fallback chain (and that the bare
  host_id.slice render is gone).
• Full api-scans + scanresult suites green; specter check 111 specs.

Verified live

The detail header now shows owas-tst01 instead of 019eccd8.

Note: one bug caught + fixed mid-implementation — COALESCE(ip_address, '')
500'd because ip_address is Postgres inet (can't COALESCE with text);
switched to host(ip_address), confirmed by the failing→passing AC-08 test.