feat: add --force-remote flag to manifest sync

[srtaalej]

Summary

• Adds --force-remote flag to slack manifest sync that pulls app settings to the local project manifest without prompting
• Symmetric counterpart to --force (which pushes local → remote)
• Validates mutual exclusion: using both --force and --force-remote returns a clear error
• Updates non-TTY remediation message to mention both force options

Context

Follow-up to #543 (two-way manifest sync). That PR's notes call out --force-remote as a planned follow-up for non-interactive "remote wins" workflows — CI pipelines, onboarding devs seeding a local manifest from deployed state, etc.

Test plan

# 1. Create a new project
  ./bin/slack create my-force-remote-test

  # 2. Install the app (creates remote manifest on app settings)
  cd my-force-remote-test
  ../bin/slack install -e manifest-sync

  # 3. Verify sync shows no differences initially
  ../bin/slack manifest sync -e manifest-sync

4. Make a local change to manifest.json (to create drift) e.g., edit display_information.description in manifest.json

  # 5. Test --force-remote pulls remote values (overwrites your local edit)
  ../bin/slack manifest sync --force-remote -e manifest-sync

  # 6. Test mutual exclusion error
  ../bin/slack manifest sync --force --force-remote -e manifest-sync

For testing remote-side drift (the more interesting case for --force-remote), edit the manifest at https://app.slack.com/app-settings after step 2, then run step 5 — it should pull the remote change into your local manifest.json without prompting.

[codecov]

Codecov Report

❌ Patch coverage is 83.33333% with 2 lines in your changes missing coverage. Please review.
⚠️ Please upload report for BASE (mwbrooks-2-way-manifest-sync@879f3a6). Learn more about missing BASE report.

Files with missing lines	Patch %	Lines
internal/manifest/sync.go	66.66%	1 Missing and 1 partial ⚠️

Additional details and impacted files

@@                       Coverage Diff                       @@
##             mwbrooks-2-way-manifest-sync     #617   +/-   ##
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  Branches                                ?        0           
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  Hits                                    ?    14259           
  Misses                                  ?     4279           
  Partials                                ?     1253           

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