feat: browse the files of a multi-file resource

[QuickMythril]

Foundation for moving Home's Git repository viewer into Explore: an app can enumerate a multi-file resource through GET_QDN_RESOURCE_METADATA and fetch each file with FETCH_QDN_RESOURCE + path, so no new Home bridge action is required.

What changed

• Multi-file browsing. The detail screen lists a resource's files and renders the selected one. Each file has its own deep-linkable route, #/detail/{service}/{name}/{identifier}/file/{path}; the identifier slot is always present in that form so a path can never be read as an identifier.
• File list is treated as untrusted input. resourceFiles() rejects absolute paths, .. traversal, backslashes, control characters, over-long paths, and caps the list, because those strings become node filepath queries and routes.
• Per-file classification. A selected file is typed by its own name; the resource-level service and mime type describe the whole publication and would mislabel, for example, a PNG inside an APP.
• Binary fetch fix. Home's bridge and Explore's browser fallback both read the node response with response.text(), so raw bytes were being re-wrapped as base64 — every thumbnail and image preview was broken. Binary reads now request encoding=base64 from Core, and the fallback forwards that parameter (only the literal base64).
• Listing grid fix. .row.resource renders five children but the grid declared four columns, so the updated timestamp wrapped to its own line. The thumbnail now has a column in both the header and the rows.

Verification

• npm ci, tsc --noEmit, 41 tests (8 files), production build — all clean.
• Rendered headlessly against the live Previewnet node, not just asserted in tests:
  • APP/Explore/Explore lists all 8 published files, with the select-a-file prompt.
  • qortium-app.json and index.html render as text/JSON with the correct row highlighted.
  • The PNG file route now emits data:image/png;base64,iVBOR… and paints; before this change the same route emitted raw \x89PNG bytes behind a ;base64, prefix.
  • An IMAGE listing renders real thumbnails on a single-line grid, and the narrow-viewport layout keeps thumbnail + identifier + status.

Version 1.4.4 → 1.4.5 (QAVS counter bump; minimum platform level is unchanged — the encoding passthrough has been in Home's bridge since the original read-only app bridge).