fix(common): fix Flow errors in nav-button component

[devin-ai-integration]

Fix Flow errors in nav-button component

This PR fixes Flow errors that were occurring when using the TypeScript-converted nav-button component in Flow files.

Changes

• Updated BackButton.js.flow to accept both Location and string for the to prop
• Updated NavButton.js.flow to make the hash property optional in the Location type
• Added .js.flow files for components that use the nav-button component to maintain Flow type compatibility

Related PR

This PR is related to #3966, which converts the nav-button component to TypeScript.

Link to Devin run: https://app.devin.ai/sessions/11a19ecf27cd4dbf856d59a802788239

[devin-ai-integration]

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[devin-ai-integration]

Closing this PR as requested. The Flow fixes will be incorporated into the original PR #3966 instead.