fix(ci): revert regression-test workspace integration

Revert regression-test to use file: protocol instead of workspace protocol.

The regression-test app uses a special import pattern (instructure-ui/ui-*/es/index)
that relies on importing from the entire packages directory structure. This pattern
is not compatible with pnpm workspace protocol which expects direct package imports.

Changes:
- Remove regression-test from pnpm-workspace.yaml
- Restore "instructure-ui": "file:../packages" dependency
- Back to 98 workspace packages (regression-test excluded)

The regression-test remains isolated from the main workspace and uses file: protocol
to link to built packages. This is the correct approach for a testing app that needs
access to the entire InstUI package structure.

Related: Fixes CI failures where regression-test couldn't resolve module paths

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Co-Authored-By: Claude <[email protected]>

Author: balzss