[ZSH] Faster startup: instant prompt, single compinit, cached probes

Re-enable p10k instant prompt (sudo-key ssh-add moved above it). Drop
oh-my-zsh.sh (second compinit, update check); set up what OMZ plugins
need ourselves. Cache java_home, go env, fzf --zsh output. Disable the
kubecontext segment (ran kubectl per shell). Log starts over 1 s to
~/.cache/zsh/startup-slow.log to catch cold-start stalls.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

zsh/.p10k.zsh_mac.example

@@ -71,7 +71,7 @@
     phpenv                  # php version from phpenv (https://github.com/phpenv/phpenv)
     scalaenv                # scala version from scalaenv (https://github.com/scalaenv/scalaenv)
     haskell_stack           # haskell version from stack (https://haskellstack.org/)
-    kubecontext             # current kubernetes context (https://kubernetes.io/)
+    # kubecontext           # off: runs kubectl on each shell's first prompt, even when hidden
     terraform               # terraform workspace (https://www.terraform.io)
     # terraform_version     # terraform version (https://www.terraform.io)
     aws                     # aws profile (https://docs.aws.amazon.com/cli/latest/userguide/cli-configure-profiles.html)