fix: use title case for manifest display names

[srtaalej]

Summary

• Manifest display names (display_information.name, bot_user.display_name, and Deno SDK Manifest({ name })) now use title case (e.g. "My App") instead of the kebab-case directory name (e.g. "my-app")
• package.json and pyproject.toml names remain kebab-case per npm/Python conventions
• Added kebabToTitleCase helper using golang.org/x/text/cases (already in go.mod)

Test plan

• Unit tests pass for kebabToTitleCase conversion
• Test_App_UpdateDefaultProjectFiles validates manifest files get title case while package.json/pyproject.toml keep kebab-case
• Test_RegexReplaceAppNameInManifest updated to reflect title-cased input
• Removed redundant "WriteFile error" test case that was identical to "manifest.json file exists"
• Manual: slack create a new app → verify manifest display name is title-cased, directory and package.json stay kebab-cased

[codecov]

Codecov Report

❌ Patch coverage is 88.88889% with 1 line in your changes missing coverage. Please review.
✅ Project coverage is 71.26%. Comparing base (7c7394c) to head (af8e3f4).

Files with missing lines	Patch %	Lines
internal/pkg/create/create.go	0.00%	1 Missing ⚠️

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #521   +/-   ##
=======================================
  Coverage   71.26%   71.26%           
=======================================
  Files         222      222           
  Lines       18682    18683    +1     
=======================================
+ Hits        13314    13315    +1     
  Misses       4188     4188           
  Partials     1180     1180           

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[zimeg]

@srtaalej Thanks for getting this started 👾 ✨

I'm hesitant on this approach and am wondering if we instead separate how arguments and flags are parsed at this point?

Some issues I ran into are in comments but I'd like to share how I think about the "create" command:

$ slack create           # Generates a random app name as current
$ slack create my-app    # Keeps path "my-app" and manifest "my-app"
$ slack create "my App"  # Uses path "my-app" and manifest "my App"

🧰 Additional cases might complicate this but it's a good time to untangle this perhaps? I'm curious also if adding the --outdir flag makes parts of this more clear, while still supporting the happiest path simple cases?

[zimeg]

🔍 issue: We might want to avoid changing the app name format altogether if this is provided in flags? Forgive me if I'm not understanding requirements right, but this app manifest for example might break with replacements:

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[zimeg]

🐍 ramble: Apps I keep might not fare well for additional example: "TIM", "TOM", or "snaek" have strange cases.