[eas-cli] Remove random branch name generation for --auto branch name non-vcs fallback

[wschurman]

Why

https://exponent-internal.slack.com/archives/C06EFBQK3B7/p1732217583248979

We should never be defaulting to a random branch name for an EAS Update. This would have disastrous consequences for usability and our interfaces, as well as for publishes and channel-branch mappings.

For workflows, this problem is more in the foreground since there's no VCS on the workflow runner.

Closes ENG-14314.

How

Remove fallback, throw an descriptive error when needed.

Test Plan

Run neas update --auto in a directory that doesn't have vcs (remove .git folder). See other error indicating that VCS is required.

Run neas branch:create, see that there's no default suggestion in the prompt.

$ neas update --auto
It looks like you haven't initialized the git repository yet.
EAS requires you to use a git repository for your project.
✔ Would you like us to run 'git init' in <dir> for you? … no
A git repository is required for building your project. Initialize it and run this command again.
    Error: update command failed.

$ neas branch:create
✖ Provide a branch name:

[wschurman]

• [eas-cli] Remove random branch name generation for --auto branch name non-vcs fallback #2747 👈 (View in Graphite)
• main

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[github-actions]

Size Change: +1.35 kB (0%)

Total Size: 53.4 MB

Filename	Size	Change
./packages/eas-cli/dist/eas-linux-x64.tar.gz	53.4 MB	+1.35 kB (0%)

_{compressed-size-action}

[codecov]

Codecov Report

Attention: Patch coverage is 12.50000% with 7 lines in your changes missing coverage. Please review.

Project coverage is 52.51%. Comparing base (751d3d1) to head (eaa9784).
Report is 1 commits behind head on main.

Files with missing lines	Patch %	Lines
packages/eas-cli/src/project/publish.ts	0.00%	5 Missing ⚠️
packages/eas-cli/src/branch/utils.ts	50.00%	1 Missing ⚠️
packages/eas-cli/src/commands/branch/create.ts	0.00%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #2747      +/-   ##
==========================================
- Coverage   52.52%   52.51%   -0.00%     
==========================================
  Files         583      583              
  Lines       22572    22576       +4     
  Branches     4445     4447       +2     
==========================================
  Hits        11854    11854              
- Misses      10683    10687       +4     
  Partials       35       35              

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[linear]

ENG-14314 Stop defaulting branch to random on `--auto` flag

[github-actions]

Subscribed to pull request

File Patterns	Mentions
**/*	@szdziedzic, @khamilowicz, @sjchmiela, @radoslawkrzemien

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[szdziedzic]

looks good to me

[github-actions]

✅ Thank you for adding the changelog entry!