Release: Postgres landing stats + latest-update board, search fixes, and dataset upload with raw ZIP support

[elainefan331]

Summary

Everything below was deployed and tested on the Zodiac dev site before this PR.

1. Landing-page stats from Postgres (refs #145)

• /dbs/stats is now served from a precomputed stats_history snapshot written at the end
  of each incremental sync (replaces the legacy CGI; no heavy query per page visit)
• dataset_changes table: dataset-level add/update/delete log written during incremental sync
• GET /dbs/updates/latest + a LatestUpdateBoard on the landing page
  (recently changed datasets, with net subject / file / size changes)

2. Search fixes

• Dataset keyword search now works together with subject filters
• The "no matching subjects" warning no longer flashes during slow searches
• New index on iolinks(dbname, dsname, view) to speed up the file-type filter

3. Dataset upload with drafts, review workflow, and raw ZIP (refs #147)

• JSON upload (/upload) for logged-in users, stored in the sandbox CouchDB as a draft
• Upload detail page: publishing settings (target database + preferred dataset ID), Submit / Withdraw, review discussion, and "View submitted JSON" through an owner-only backend proxy
• Dashboard → Uploads tab with status and raw ZIP chips
• Raw ZIP upload: resumable (tus) from the browser directly to a new storage-api/
  service on Zodiac; pause/resume, resume after reload, cancel, server-side verification
  (size, ZIP check, SHA-256)
• Upload tokens, HMAC-signed backend ↔ storage calls, push + pull (reconciler) completion