Backport #916 to v26-branch: Don't require a TTY for non-interactive composer server commands

[mikelittle]

Manual backport of #916 to v26-branch. The auto-backport bot couldn't apply this because v26-branch has a case null: arm in db() that was restructured to default: on master.

Why backport

On GitHub Actions there is no controlling TTY, so the hardcoded docker exec -it … -db in composer server db exec errors with the input device is not a TTY before the SQL runs. The product-dev nightly CI uses this path indirectly via composer dev-tools codecept's test-DB bootstrap (DROP DATABASE … CREATE DATABASE test;…), so the test/test2 DBs never get created and codecept then fails with [1044] Access denied for user 'wordpress'@'%' to database 'test' for every module suite. Travis didn't hit this because its runner supplied enough of a pseudo-TTY for -it to work.

What changed

Same shape as #916 against master, adapted for v26's slightly older db() body:

• composer server db exec / s3 import-uploads / s3 exec drop -t and only pass -i so they run without a controlling terminal.
• composer server db (interactive REPL on this branch is case null:), shell, and the logs service picker keep -it and gate on a new require_tty() that prints a clear error and a non-interactive alternative when no terminal is attached, instead of hanging or crashing on Docker's opaque error.
• Adds is_tty() / require_tty() helpers.

The db case on this branch differs from master:

• master collapsed case null (REPL) and default (unknown subcommand) into a single default arm with the non-interactive -e/--execute/-B/--batch detection inside.
• v26 still has separate case null and default arms, and the REPL path doesn't take extra options, so the -e/-B detection isn't needed here — the REPL is always interactive on this branch. Kept that simpler shape; just guarded case null with require_tty().

Test plan

• Trigger product-dev nightly against v26 after merge and confirm Altis 26 jobs no longer hit "Access denied for user 'wordpress'@'%' to database 'test'".
• Manual: composer server db exec -- "SELECT 1; " works without a TTY (e.g. piped through <&-).
• Manual: composer server db with a TTY still opens the interactive REPL.

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