Cache localhost hostname to eliminate Tab key sluggishness

- Add cached localhost field to TuiApp struct to avoid repeated gethostname() system calls
- Initialize localhost once in constructor instead of calling gethostname() on every navigation
- Replace gethostname() calls in update_hosts() and navigate_host() with cached value
- Eliminate expensive system call bottleneck causing Tab key responsiveness issues
- Reduce Tab navigation from 2+ system calls to zero system calls (memory access only)
- Fix performance regression introduced by immediate UI refresh implementation
- Bump version to 0.1.60

shared/Cargo.toml

@@ -1,6 +1,6 @@
 [package]
 name = "cm-dashboard-shared"
-version = "0.1.59"
+version = "0.1.60"
 edition = "2021"
 
 [dependencies]