feat: PostgreSQL search, AutoBIDSify, Express API proxy, and 2D chart responsive fix

[elainefan331]

Summary

Search — migration from CGI to PostgreSQL

• Replaced CGI-based search with PostgreSQL queries backed by ioviews and iolinks tables
• Added incremental sync script to populate search tables from CouchDB with transactions and concurrency
• Added modality filter (AND/OR mode), file type filter, age-range slider, subject count range, task/session/run
  keyword fields, and run count display on subject cards
• Show matching files in dataset card
• File download endpoints with Mac/Linux and Windows script options; three script formats on dataset detail page

Express backend API proxy

• Routed all external API calls through Express server

AutoBIDSify

• Added private mode autobidsify page with local AI provider support (Ollama / LM Studio / Jan) — configurable base URL and custom model name
• Use qwen3.6:27b on the NeuroJSON Ollama server; added auth-gated endpoint
• UI improvements: renamed buttons, tooltips, file tree section title, output panel status messages, timestamped
  output folders

2D plot

• Fixed chart overflowing on small screens — reads container width on render and resizes via ResizeObserver

Closes #125