feat: add --manifest-source flag to run and deploy commands

[srtaalej]

Summary

• Adds a --manifest-source=project|remote flag to slack run and slack deploy commands
• When manifest sync detects differences during run/deploy, this flag allows non-interactive resolution without requiring slack manifest sync to be run separately
• Skips the "Overwrite manifest on app settings?" confirmation prompt during install when --manifest-source is set — project auto-approves the overwrite, remote skips it entirely
• Updates the non-TTY error remediation to reference --manifest-source instead of --force/--force-remote (which are only available on manifest sync)

Closes #628

Test plan

• make lint passes
• make test passes
• Manual test: slack run --manifest-source=project pushes local manifest without prompting
• Manual test: slack run --manifest-source=remote pulls app settings without prompting
• Manual test: slack deploy --manifest-source=project works in non-TTY (CI) environments
• Manual test: slack run --manifest-source=invalid returns a clear validation error
• Manual test: slack run --manifest-source=remote skips the "Overwrite manifest?" prompt on reinstall

[codecov]

Codecov Report

❌ Patch coverage is 91.30435% with 2 lines in your changes missing coverage. Please review.
✅ Project coverage is 78.20%. Comparing base (73dde37) to head (d327435).

Files with missing lines	Patch %	Lines
internal/pkg/apps/install.go	50.00%	2 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #630      +/-   ##
==========================================
+ Coverage   78.18%   78.20%   +0.01%     
==========================================
  Files         239      239              
  Lines       18136    18157      +21     
==========================================
+ Hits        14179    14199      +20     
- Misses       3957     3958       +1     

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[zimeg]

@srtaalej I appreciate the most patient request for review 🙏 ✨ I'm requesting a few changes with hopes these comments move this in evermore stable directions. I call out:

• Removing --force-remote flag altogether alongside this change: I'd like to avoid multiple options unless follow up is planned to remove this too?
• Favoring the existing terms and implementations of manifest source: Our configuration file has some logic we might reuse here!

If I can share more to these please let me know! I'm optimistic we include this in upcoming release 🚀 🔮

[zimeg]

🪓 question: Are we alright to replace the --force and --force-remote options altogether while the sync command is under experiment?

[zimeg]

🧮 suggestion: Let's keep this in alphabetical order!

[zimeg]

Suggested change

	const (
	ManifestSourceProject = "project"
	ManifestSourceRemote = "remote"
	)
	const (
	ManifestSourceProject = "local"
	ManifestSourceRemote = "remote"
	)

🪬 suggestion(blocking): Earlier suggestion might've hinted at "project" terms but we should match existing configuration options I realize. Perhaps reusing logic from this package instead of validations here?

slack-cli/internal/config/manifest.go

Lines 20 to 23 in 73dde37

	const (
	ManifestSourceLocal ManifestSource = "local"
	ManifestSourceRemote ManifestSource = "remote"
	)

[zimeg]

Suggested change

	if err := cmdutil.ValidateManifestSourceFlag(clients); err != nil {
	return err
	}

🪓 quibble: I'd favor this validation happening with the switch case in internal/manifest/sync.go to avoid duplicate checks in code, although I understand this might error earlier.