fix: ignore whitespace in store plugin search

[zdennisz]

Please tick as appropriate:

• I have tested this code on a steam deck or on a PC
• My changes generate no new errors/warnings
• This is a bugfix/hotfix
• This is a new feature

Description

The plugin store search used plain substring matching, so a query like tab master would not match a plugin named tabmaster. This normalizes both the search query and the searched fields (name, description, author, tags) by lowercasing and stripping whitespace before comparing.

Store search is performed entirely client-side (the remote store API returns the full list; only sort_by/sort_direction are sent), so this fix is contained to frontend/src/components/store/Store.tsx.

Verification

• pnpm run typecheck — clean
• prettier — clean
• Logic check: tab master, tabmaster, css, cssloader all match TabMaster/CSS Loader; empty query still returns all plugins.

Resolves #622