Fix doc typos, add changelog formatter for GitHub releases

[theoephraim]

Summary

• Fix GitHub releases having no body content — previously, GitHub releases used a basic fallback that produced minimal output. Now the configured changelog formatter is used for GitHub release bodies too, with a new target context field so formatters can customize output per target (e.g., omit date headings for GitHub releases since the release already has a timestamp).
• Fix typos across docs: "additonal", "Oending", "settting", awkward phrasing in cli.md
• Change bun test to bun run test in README development section
• Add "claude" to AI setup targets in CLI help text (was missing despite being a valid target)

Test plan

• Verify GitHub releases use the changelog formatter and include full content
• Verify docs read correctly with no typos
• Run bunx bumpy --help and confirm claude appears in AI setup targets

[bumpy-bot]

The changes in this PR will be included in the next version bump.

Patch releases

• @varlock/bumpy 1.2.2 → 1.2.3

Bump files in this PR

• docs-typos-and-fixes.md (view diff) (edit)

Click here if you want to add another bump file to this PR

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This comment is maintained by bumpy.