Stop the post-start hook prompting and hanging ddev start

[mortona42]

Fixes #21.

From claude:

The README says the post-start hook runs ddev claude-update in report-only mode, but the hook passed no flags and the command's "am I interactive?" guard was only [ -t 0 ]. Inside a DDEV exec-host hook stdin is still a tty, so the guard passed and the command printed its [i/p/c] menu and blocked on read -- freezing the ddev start that spawned it (and, when the start was triggered implicitly, the ddev claude behind it). Answering did not free it: [i] shells out to a nested ddev exec and [p] execs ddev restart --no-cache, both from inside a start still in progress.

CI never caught it because bats runs with stdin on a pipe, where the old guard happened to do the right thing.

• Pass -n in the hook so the documented report-only behaviour is what the hook actually asks for, rather than a side effect of tty detection.
• Require a tty on stdout as well as stdin before prompting, so any other caller that captures our output degrades to a report instead of hanging.
• Let DDEV_CLAUDE_CODE_AUTOUPDATE override -n, so opting into auto-updates still works now that the hook passes that flag.
• Cover the env-var-beats--n path in tests/test.bats.

The Issue

• Fixes #REPLACE_ME_WITH_RELATED_ISSUE_NUMBER

How This PR Solves The Issue

Manual Testing Instructions

ddev add-on get https://github.com/FreelyGive/ddev-claude-code/tarball/refs/pull/REPLACE_ME_WITH_THIS_PR_NUMBER/head
ddev restart

Automated Testing Overview

Release/Deployment Notes