fix: source Interests top-level nav label from feature/interests module

[Noahs212]

Summary

• Switch INTERESTS in app/.../navigation/TopLevelNavItem.kt from searchR.string.feature_search_api_interests to interestsR.string.feature_interests_api_title. The previously-orphaned feature_interests_api_title resource (added on 2025-11-19 in 068d8cc during the api/impl module split, never wired up) is now the source of truth for the Interests bottom-nav label.
• Restores the per-module-ownership pattern used by the sibling FOR_YOU / BOOKMARKS entries.
• Eliminates the silent cross-feature coupling: changing the in-search "Interests" link copy at SearchScreen.kt:248 no longer also rewrites the bottom-nav tab.
• Updates NavigationTest.kt to read the interests label from the interests module's resource, matching the production change.

User-visible behavior is unchanged — both strings have the value "Interests", so existing tests, screenshots, and snapshots stay green. The feature_search_api_interests resource in the search module is untouched and still used by SearchScreen.kt:248 and SearchScreenTest.kt:83.

Fixes #2112

Test plan

• ./gradlew spotlessApply
• ./gradlew :app:assembleDemoDebug
• ./gradlew :app:lintDemoDebug
• ./gradlew :app:connectedDemoDebugAndroidTest --tests "*NavigationTest*" (needs emulator/device)
• Manually verify the Interests bottom-nav tab still reads "Interests" on a launched debug build.

[gemini-code-assist]

Code Review

This pull request updates the 'Interests' navigation item and its associated UI tests to use string resources from the interests feature module instead of the search feature module. This involves updating imports and resource references in TopLevelNavItem.kt and NavigationTest.kt to improve modularity. I have no feedback to provide as the existing review comments were purely explanatory and did not identify any issues or improvement opportunities.