refactor(shell): thin stubs with managed ~/.config/zsh tree

Split always-on PATH/env, login hooks, and interactive UX into a
managed tree under ~/.config/zsh, with never-overwrite local/ hooks.
Agents and interactive shells share one PATH owner; deploy.sh applies
the layout safely across machines.

local/env.local.zsh.example

@@ -0,0 +1,4 @@
+# Copy to ~/.config/zsh/local/env.local.zsh (installer never overwrites local/).
+# Runs for every zsh after managed env modules.
+#
+# . "$HOME/.cargo/env"

local/interactive.local.zsh.example

@@ -0,0 +1,2 @@
+# Copy to ~/.config/zsh/local/interactive.local.zsh (installer never overwrites local/).
+# Interactive only, after oh-my-zsh and managed post-omz aliases.

local/login.local.zsh.example

@@ -0,0 +1,3 @@
+# Copy to ~/.config/zsh/local/login.local.zsh (installer never overwrites local/).
+# Login shells only: OS/vendor hooks (OrbStack, MacPorts, product installers).
+# Do not put primary user-tool PATH here; that belongs in env/00-path.zsh.