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

Cargo.lock

@@ -270,7 +270,7 @@ checksum = "a1d728cc89cf3aee9ff92b05e62b19ee65a02b5702cff7d5a377e32c6ae29d8d"
 
 [[package]]
 name = "cm-dashboard"
-version = "0.1.58"
+version = "0.1.59"
 dependencies = [
  "anyhow",
  "chrono",
@@ -292,7 +292,7 @@ dependencies = [
 
 [[package]]
 name = "cm-dashboard-agent"
-version = "0.1.58"
+version = "0.1.59"
 dependencies = [
  "anyhow",
  "async-trait",
@@ -315,7 +315,7 @@ dependencies = [
 
 [[package]]
 name = "cm-dashboard-shared"
-version = "0.1.58"
+version = "0.1.59"
 dependencies = [
  "chrono",
  "serde",