feat: implement abrdn ETF feed and sibling-identical watchlist

[daggerok]

Summary

• Rebuild from the supplied self-contained Aberdeen plan; original work was not present on GitHub.
• Copy the pinned JPMorgan UI with only permitted brand/source substitutions; reverse-substitution SHA256 tests enforce parity.
• Official Aberdeen gateway catalog, NAV, fund facts, complete paginated securities holdings, and month-/quarter-end NAV returns.
• SEC N-PORT fallback with series identity validation; Yahoo daily market history/dividends; previous-data retention.
• Persist defaults in update-config.json; primary CONCURRENCY/TICKERS Actions inputs plus safe advanced JSON (25-input platform limit).
• Standard Dependabot, weekly/manual updater workflow, README, topics and About.

Validation

• 37 tests / 90 assertions passing; Bun updater/app bundling; frozen lock install; actionlint clean.
• Live full feed: 11 ETFs / 328 securities holdings / 27,067 history rows.
• Two consecutive full runs produced byte-identical API files.
• Isolated full-feed outage (every issuer/SEC/Yahoo request returns 403) preserved all API files byte-for-byte.
• Chromium smoke: checkbox-only selection, catalog, holdings, history, distributions, watchlist, CSV, dark mode and search.

Limitations / review notes

• Live SEC retrieval is blocked with 403 in this environment; parser and wrong-series rejection are fixture-tested, not claimed as live SEC success.
• Five physical metals trusts expose no securities-holdings tab; marked not-applicable, no invented bullion positions.
• History/dividends use Yahoo; do not represent these as official NAV history. Yahoo can revise actual upstream values, including volume.
• GitHub-hosted workflow execution and Pages deployment remain pending the default-branch publication/settings.
• plan.txt contains checkpoints and verified findings; .plans/ preserves original instructions and approved adaptations.

Owner review required: do not merge this Aberdeen PR automatically.
Sibling README-only PRs are separately authorized for merge.