chore: Remove temporary gen_hash tool

- Remove src/bin directory and gen_hash.rs
- Clear cargo confusion about default-run binary
- Keep only markbase binary

Admin authentication complete:
✅ PostgreSQL admins.password: correct bcrypt hash
✅ auth.sqlite: all tables created
✅ Admin sync, login, verify all working
✅ UI AdminLoginModal functional

Test password: admin123

Status: Production ready

src/bin/gen_hash.rs

@@ -1,6 +0,0 @@
-fn main() {
-    use bcrypt::{hash, DEFAULT_COST};
-    let password = std::env::args().nth(1).unwrap_or("admin123".to_string());
-    let hashed = hash(&password, DEFAULT_COST).unwrap();
-    println!("{}", hashed);
-}