docs: add missing CI flags and clarify defaults in installation page

[bmarianome]

✅ Checklist

• [✅] I have followed every step in the contributing guide (updated 2022-10-06).
• [✅] The PR title follows the convention we established conventional-commit
• [✅] I performed a functional test on my final commit

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Changelog

I changed the docs to explain clearly the defaults when using the CI mode and not specifying any of the options.

Also, the docs didn't specify there's flags for some of the options like the import alias and eslint.

I was forking to create the flags when reading the code found out they exist.

Please add :) I created, idk, +200? t3 apps manually because I wasn't aware of this 🙃

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Project	Deployment	Actions	Updated (UTC)
create-t3-app	Ready	Preview, Comment	Feb 21, 2026 3:44pm

[bmarianome]

Opened an issue #2215 because even though they exist, import alias is not working