fix(summer): pass the app binary's exit code through and print its error once

- bonfire.WithExitCode (additive) makes an error carry the exit code
  bonfire.Execute returns; a code outside 1..255 gives 1
- runAppCmd, factored out of runAppBinary, returns
  Reported(WithExitCode(err, code)) when the binary exited with a code, so
  summer prints no second error block; a binary killed by a signal keeps
  summer's block and exit 1
- README, console introduction and upgrading notes say so (CR-02)

docs/setup/upgrading.md

@@ -43,6 +43,7 @@ Applications pin exact versions, so a new release never reaches an application u
 - **Exit codes.** A failed command exits 1 and a usage error (an unknown command or flag, a wrong number of arguments) exits 2. Errors print as a block on stderr with a hint where the framework knows the fix, and `-v` shows the wrapped errors.
 - **`-q` keeps data.** `-q` hides information and success lines, spinners and progress bars, but still prints what a command exists to produce: the token of `admin:token:create`, the key of `key:generate` and every `--json` output.
 - **Production confirmation.** `migrate`, `migrate:rollback`, `deferred:purge` and `queue:clear` ask before they run when the environment is `production` and they run on an interactive terminal; `--force` skips the question. Off a terminal, as in deploy scripts over SSH, nothing changes.
+- **`summer` delegates keep the binary's exit code.** Since 0.4.2 `summer migrate`, `summer serve` and the other delegated commands exit with the app binary's exit code and print only the binary's error block; 0.4.0 and 0.4.1 printed a second block and exited 1.
 - **`summer dev` runs `serve`.** It used to start the binary without a command, which printed the help and stopped; it now runs `bin/<app> serve` with the global options you give `summer dev`.
 - **Result lines.** `summer build` ends with `Built bin/<app> in <time>`, the `make:` commands print `Created <path>` per file, `migrate` prints `Applied N migrations` or `Nothing to migrate`, and `queue:clear` prints `Cleared N jobs from <queue>`. Adjust scripts that matched the old lower-case lines.