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/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.