fix(core): harden kill-process, network diagnostics, ssh key setup, and disk health

[ashishsinghbora]

Summary

kill-process.sh

• Guard against terminating init (PID 1), PID 0, self ($$), and parent ($PPID).
• Filter out $$ and $PPID from pgrep matching results.
• Validate signals with kill -l and handle missing arguments.

network-diagnostics.sh

• Standardize status badges: [PASS], [FAIL], [UNKNOWN], [SKIPPED].
• Avoid false positive failures for firewall-filtered ping and gateway ports.
• Provide a summary report with pass/fail/skip counts.

ssh-key-setup.sh

• Automatically create a timestamped backup before overwriting any existing key.
• Generate RSA with 4096-bit strength by default when RSA is chosen.
• Add passphrase argument (-p / --passphrase) and enforce strict 0700/0600 file permissions.

disk-health.sh

• Support targeted device checking via [device] argument.
• Distinguish virtual/container devices without SMART support.
• Detect root/sudo permissions for raw device access.

Verification

• Tested PID 1 and self termination rejection.
• Tested killing background child processes safely.
• Tested SSH key generation, permission checks, overwrite refusal without force, and backup preservation.
• Tested network diagnostics summary report.
• Verified ShellCheck passes without warnings.
• Verified test suite passes.

[ashishsinghbora]

Code review: verified process termination safety excludes PID 1/self/parent, network diagnostics produces clean status badges, SSH key setup creates automatic backups and secures permissions, and disk health handles device targeting and VM/container environments.