[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/.zsh_plugins.txt

@@ -1,5 +1,4 @@
-# Load OMZ plugins
-ohmyzsh/ohmyzsh
+# Load OMZ lib and plugins; not oh-my-zsh.sh itself (own compinit, theme, update check)
 ohmyzsh/ohmyzsh path:lib
 ohmyzsh/ohmyzsh path:plugins/git
 ohmyzsh/ohmyzsh path:plugins/golang