Add theme-set/switching logic, and minor nvim, tmux, obsidian changes

src_files/.local/scripts/theme-update-neovim

@@ -0,0 +1,10 @@
+#!/bin/zsh
+
+nvim_stdpath_run=$(dirname $(nvim -l <(echo "vim.cmd.echo('stdpath(\"run\")')") > /dev/stdout 2>&1))
+find "$nvim_stdpath_run" -type s -name "nvim*" 2> /dev/null |
+while IFS= read -r nvim_server; do
+    timeout 2s nvim --server "$nvim_server" \
+        --remote-expr "execute('lua ThemeUpdate()')" \
+        > /dev/null 2>&1
+done
+