feat(auth): add --region flag to signup and login

[LorrisSaintGenez]

What

• auth signup and auth login accept --region for the first application created when the account has none.
• When no region is given and the CLI can't prompt (no TTY), the region picker is replaced by an actionable error — no region specified; pass --region (e.g. EU, UK, USC, USE, USW) — instead of dying on EOF. Makes sign-up completable from scripts and agents.

Test

algolia auth signup --help          # --region listed
algolia auth login --help           # --region listed
algolia auth signup --app-name "Demo" --region EU   # on a fresh account: first app created in EU, no region prompt

[codacy-production]

Up to standards ✅

🟢 Issues 0 issues

Results:
0 new issues

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🟢 Metrics 0 complexity · 3 duplication

Metric	Results
Complexity	0
Duplication	3

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_{TIP This summary will be updated as you push new changes.}