Codex is per-project, not machine-wide

The installer cannot run `--runtime codex` for you: the verb requires a
project, since one of its targets is the project's own AGENTS.md. It now
detects codex and prints the command to run in each project instead.

Signed-off-by: disqualifier <dev@disqualifier.me>

README.md

@@ -31,17 +31,23 @@ already set up prints status and changes nothing.
 | --- | --- |
 | `--skill-only` | skill and hooks only; no daemon, no service |
 | `--no-node` | never provision Node; falls back to skill-only if yours is too old |
-| `--no-codex` | don't wire Codex, even if it's installed |
+| `--no-codex` | don't mention Codex, even if it's installed |
 | `--registry <url>` | install from somewhere other than the default registry |
 | `--yes` | don't prompt |
 
 Node 20 is the floor for single mode. The daemon needs 22.13 or newer, because
 it uses `node:sqlite` without a flag.
 
-Claude Code gets wired up either way. If `codex` is on your PATH that gets
-wired too — hooks, the skill, and a marked block in your project's `AGENTS.md`.
-If it isn't installed, nothing is written for it. `--no-codex` skips it on a
-box that does have it.
+Claude Code gets wired up machine-wide here. **Codex is per-project** — one of
+the things it writes is a block in the project's own `AGENTS.md` — so the
+installer can't do it for you. If `codex` is on your PATH, the installer says
+so and prints the command; run it inside each project you want Codex in:
+
+```sh
+standup install --runtime codex
+```
+
+`--no-codex` tells the installer not to mention it.
 
 Windows uses the same flags with PowerShell spelling: `-SkillOnly`, `-NoNode`,
 `-NoCodex`, `-Registry <url>`, `-Yes`.