Add --non-interactive flag to all commands and improve CI/headless UX

[ejacquier]

Problem

AI agents and CI/CD pipelines encounter "could not open a new TTY" errors (22+ occurrences in error tracking) when commands try to prompt interactively. Only cre init and cre workflow simulate had --non-interactive support. Additionally, cre login --help didn't mention CRE_API_KEY as the headless auth method.

Changes:

cre login improvements

• Updated help text to document CRE_API_KEY as the CI/headless auth method (referencing app.chain.link).
• Added --non-interactive flag that returns an actionable error directing users to set CRE_API_KEY.

Global TTY guard in root.go

• Before the "Would you like to login now?" prompt, detect non-TTY stdin via term.IsTerminal().
• Non-interactive environments now get a clear error with CRE_API_KEY guidance instead of hanging.

--non-interactive flag is now global

• Commands with interactive prompts (workflow deploy/delete/custom-build, account link-key/unlink-key) validate that required skip flags (--yes, --force, --owner-label) are provided, erroring with specific missing-flag suggestions.
• Commands without prompts (workflow activate/pause, secrets create/update/delete/list) accept the flag for forward-compatibility.

[github-actions]

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