Fix folder picker navigation and project opening

[yaacovcorcos]

Summary

• make Enter open the directory shown in the path field, even when that directory contains child folders
• make the upper-left arrow move to the parent directory one level at a time, returning to the source cards only from the initial local location
• rename the local action from Add to a blue Open action and retain neutral styling for New folder
• allow creating a collision-safe child directory from any browsed local folder before starting the project setup flow
• keep Arrow Right as the explicit keyboard action for entering a highlighted directory
• tighten the follow-up project setup dialog into two compact, aligned choices with a smaller ready-state modal

Root cause

The path query reset React's highlighted value when navigating, but the Base UI command list retained its internal active index. Enter then reached both the input handler and the command-list handler, so a highlighted child (or parent entry) could win over the directory displayed in the input. Leaf directories appeared to work because there was no child selection to conflict with the open action.

This change captures Enter at the input boundary and always resolves the displayed path. Browsing highlighted entries is now explicit with Arrow Right, and the command selection state resets whenever the browsed directory changes.

Verification

• bun install --frozen-lockfile
• bun run fmt:check
• bun run lint (0 errors; existing warnings only)
• bun run typecheck
• bun run test
• bun run build:desktop
• bun run --cwd apps/web test:browser:stable

Focused browser coverage verifies the non-leaf Enter behavior on mocked macOS, Linux, and Windows paths, one-level back navigation, Arrow Right browsing, new-folder creation, and compact desktop setup-choice geometry. The complete stable browser suite passed (48 files, 258 passing tests, 11 skipped).

Manual journey

Validated against isolated real server and web processes with nested directories:

• opened Parent while Child was visible and confirmed the project setup received Parent, not Child
• moved from Parent/Child back to Parent with the upper-left arrow without leaving the picker
• created Empty/New folder, confirmed the directory existed before setup preview, and opened it as an empty project
• completed both setup outcomes and confirmed Scient setup created .scient/, PROJECT.md, and AGENTS.md
• reviewed the same populated Parent folder before and after the UI change at desktop width
• reviewed the compact ready-state setup choices at desktop width and confirmed the responsive mobile stack remains usable

The test matrix covers path semantics for macOS, Linux, and Windows; hosted native-platform CI remains authoritative for OS integration.

Screenshots

Before and after folder-picker screenshots plus the compact setup-choice screenshot were captured during the manual journey and are ready to attach after file-upload approval.