feat: add local override hooks for zsh and git

~/.zshrc.local and ~/.gitconfig.local hold machine-specific settings
(secrets, work identity, installer PATH additions) so third-party
installers stop dirtying the tracked configs.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

.gitconfig

@@ -53,3 +53,9 @@ default = simple
 [core]
 editor=nvim
 pager = less -x4
+
+# Machine-specific overrides (e.g. a work identity via includeIf).
+# Git silently skips this if the file doesn't exist. Keep last so
+# local settings win.
+[include]
+path = ~/.gitconfig.local

.zshrc

@@ -128,3 +128,8 @@ fi
 export NVM_DIR="$HOME/.nvm"
 [ -s "$NVM_DIR/nvm.sh" ] && \. "$NVM_DIR/nvm.sh"
 [ -s "$NVM_DIR/bash_completion" ] && \. "$NVM_DIR/bash_completion"
+
+# Machine-specific overrides (secrets, work proxies, installer PATH
+# additions). Never tracked in the repo — keep this line last so local
+# settings win.
+[ -f "$HOME/.zshrc.local" ] && source "$HOME/.zshrc.local"