Implement CSV import functionality for tags in TagPage

[ngAlexander9]

Description

Designed around the expected UX of adding tags from a csv file formatted similarly to consolidated.csv and derived from the similar PV import UX. Handles duplicates, adding new tag groups.

Requires: slaclab/react-squirrel-backend#47

Recording.2026-03-24.133205.mp4

I tested this with consolidated.csv and a truncated version (first couple thousand lines of consolidated.csv)

Motivation

Screenshots

Pre-merge checklist

• Code works interactively
• Code follows the style guide
• Code contains descriptive docstrings
• New/changed functions and methods are covered in the test suite where possible
• Test suite passes locally
• Test suite passes on GitHub Actions

[shilorigins]

I tried rebasing this onto ang/csv-parsing / updated main to test compatibility, and I'm running into some issues. If I try pnpm dev, then I get a white screen. If I change parseCSVToPVs to parseCSVToPVsAsync then I get an interactive UI, but attempting to import tags from consolidated.csv gives: Failed to read CSV file: can't access property "length", result.errors is undefined. pnpm build also fails on the original branch as well as my rebased version, which may indicate where those errors will crop up. Can you check this branch's compatibility with recent updates to react-squirrel and react-squirrel-backend?

[shilorigins]

Tested with slaclab/react-squirrel-backend#47, importing tags from a csv with 1000 rows and then 35,000 rows was responsive and caught duplicates accurately. This functionality is great to have, thanks!