refactor(shell): collapse managed tree back into stubs

Drop ~/.config/zsh/{env,interactive,login} modules. PATH and local.zsh
live in .zshenv; interactive UX is a single .zshrc again. Deploy only
installs the three stubs and removes obsolete trees/examples.

local.zsh.example

@@ -1,6 +1,4 @@
-# Copy to ~/.config/zsh/local.zsh (deploy never overwrites local.zsh).
-# Sourced from ~/.zshenv after managed env modules — every zsh sees this,
-# including non-interactive agent shells.
+# Copy to ~/.config/zsh/local.zsh (deploy never overwrites it).
+# Sourced from ~/.zshenv — every zsh sees this, including agents.
 #
 # . "$HOME/.cargo/env"
-# source ~/.orbstack/shell/init.zsh 2>/dev/null || :