Add work-specific configs and enhance git/shell setup

- Add modular zsh configs: zshrc-dev for dev tools, zshrc-natera for work
- Add .gitignore to exclude private Natera config from version control
- Configure git commit signing and delta diff viewer in gitconfig
- Regenerate p10k.zsh with rainbow theme and improved visual settings
- Add HIST_IGNORE_SPACE option to prevent saving sensitive commands
- Document Natera machine setup with private config template in README

gitconfig

@@ -1,6 +1,7 @@
 [user]
 	name = Eric Wagoner
 	email = ewagoner@gmail.com
+	signingkey = F43B105D9B88A97F
 [credential]
 	helper = osxkeychain
 [mergetool]
@@ -15,6 +16,7 @@
 	required = true
 [core]
 	excludesfile = ~/.gitignore_global
+	pager = delta
 [alias]
 	co = checkout
 	ci = commit
@@ -49,3 +51,18 @@
 # Use work email for repos under ~/work/
 [includeIf "gitdir:~/work/"]
 	path = ~/.gitconfig-work
+[commit]
+	gpgsign = true
+
+[interactive]
+	diffFilter = delta --color-only
+
+[delta]
+	navigate = true
+	light = false
+	side-by-side = true
+	line-numbers = true
+	syntax-theme = Dracula
+
+[merge]
+	conflictstyle = diff3