feat(tui): default sessions to current repo scope

[samzong]

What's changed?

• Add a persisted default_current_repo_scope TUI setting.
• Default the TUI session scope to the current GitHub repo identity when enabled.
• Keep manual project filters path-based and clear repo scope when a path is selected.

Why

• Multiple worktrees for the same repo should share the default Recall session view instead of being split by filesystem path.

Verification

• git diff --cached --check
• make check
• pre-ship committed diff scan: MUST-FIX 0, deferred 0