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 79.16667% with 5 lines in your changes missing coverage. Please review.
✅ Project coverage is 72.35%. Comparing base (bd2741b) to head (4837889).

Files with missing lines	Patch %	Lines
cmd/platform/deploy.go	33.33%	2 Missing ⚠️
cmd/platform/run.go	33.33%	1 Missing and 1 partial ⚠️
internal/pkg/apps/install.go	50.00%	0 Missing and 1 partial ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #630      +/-   ##
==========================================
- Coverage   72.38%   72.35%   -0.03%     
==========================================
  Files         238      238              
  Lines       20072    20088      +16     
==========================================
+ Hits        14529    14535       +6     
- Misses       4275     4280       +5     
- Partials     1268     1273       +5     

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