fix(shell): use single ~/.config/zsh/local.zsh for machine local

Replace the local/ directory of split env/login/interactive files with
one always-on local.zsh sourced from .zshenv. Deploy migrates old
fragments and never overwrites local.zsh.

README.md

@@ -27,8 +27,7 @@ every zsh                login only              interactive only
 ──────────               ──────────              ────────────────
 ~/.zshenv (stub)         ~/.zprofile (stub)      ~/.zshrc (stub)
   → config/zsh/env/*       → config/zsh/login/*    → config/zsh/interactive/*
-  → local/env.local.zsh    → local/login.local.zsh → ~/.config/zshrc/* (before omz)
-                                                   → local/interactive.local.zsh
+  → config/zsh/local.zsh                           → ~/.config/zshrc/* (before omz)
 ```
 
 PATH for user tools is built **once** in `~/.config/zsh/env/00-path.zsh`
@@ -41,7 +40,7 @@ PATH for user tools is built **once** in `~/.config/zsh/env/00-path.zsh`
 | `~/.config/zsh/env/` | Managed always-on env (PATH, Homebrew) | Overwritten |
 | `~/.config/zsh/interactive/` | Managed interactive UX (omz, aliases) | Overwritten |
 | `~/.config/zsh/login/` | Managed login hooks (usually empty) | Overwritten |
-| `~/.config/zsh/local/*` | Machine-local env/login/interactive | **Never overwritten** |
+| `~/.config/zsh/local.zsh` | Machine-local overrides (every zsh) | **Never overwritten** |
 | `~/.config/zshrc/*.zsh` | Personal/tool overlays (before omz) | Left alone |
 | `~/.local/bin/` | User tools + intentional shims (e.g. `grok`) | Left alone |
 
@@ -50,18 +49,12 @@ other tools). Link wanted entrypoints into `~/.local/bin` instead.
 
 ## Personal configuration
 
-### Always-on (agents see this)
+### Machine-local (agents see this)
 
 ```bash
-# ~/.config/zsh/local/env.local.zsh
+# ~/.config/zsh/local.zsh
 . "$HOME/.cargo/env"
-```
-
-### Login only (vendor hooks)
-
-```bash
-# ~/.config/zsh/local/login.local.zsh
-# OrbStack, MacPorts, product installers — not primary PATH policy
+source ~/.orbstack/shell/init.zsh 2>/dev/null || :
 ```
 
 ### Interactive overlays (before oh-my-zsh)
@@ -81,4 +74,4 @@ curl -fsSL https://git.miomio.moe/mio/easyzsh/raw/branch/master/patch.sh | bash
 Current fragments: `fnm`, `nvm`, `pyenv`, `p10k`, `merlin_devbox`, `merlin_worker`.
 
 Aliases that must beat oh-my-zsh belong after omz loads (see managed
-`interactive/20-post-omz.zsh`) or in `~/.config/zsh/local/interactive.local.zsh`.
+`interactive/20-post-omz.zsh`).