fix: Create project modal closes on accidental backdrop clicks

[Roshan931]

Fixes #23

Root cause

Backdrop click handler unconditionally closes CreateProjectModal

Changes

• Track user edits (name typed or template tile picked) in CreateProjectModal and ignore backdrop clicks while the form is dirty; explicit exits (X, Cancel, Escape) still close. Backdrop handler now also ignores clicks that originate inside the dialog. Added a vitest regression suite covering both closing and non-closing paths.