Integrate Riverpod-based navigation state management

[dhruvi-16-me]

Summary

This PR migrates HomeScreen navigation state from local widget state to Riverpod.

Changes

• Added a typed HomeTab enum for home navigation state
• Replaced local _selectedIndex state with Riverpod-managed navigation state
• Introduced homeTabProvider as the single source of truth for tab selection
• Updated HomeScreen to consume and update navigation state through Riverpod
• Preserved existing IndexedStack-based screen architecture
• Preserved existing route argument handling (screen and initial_message)
• Removed obsolete HomeScreen navigation-related dead code

Motivation

This change establishes a centralized navigation state layer using Riverpod and prepares the codebase for upcoming routing work, including:

• go_router integration
• URL-based navigation
• Browser history support
• Deep linking

By moving navigation ownership out of local widget state, future routing changes can be implemented without restructuring HomeScreen navigation logic again.

Notes

• This PR intentionally does not introduce go_router
• This PR intentionally does not add URL synchronization, browser history handling, or deep linking
• Existing screen implementations and navigation behavior remain unchanged

Testing

• Verified tab switching across all HomeScreen tabs
• Verified route argument handling for screen navigation
• Verified chat initialization via initial_message

✅ Checklist

• I have read the contributing guidelines.
• I have added tests that prove my fix is effective or that my feature works.
• I have added necessary documentation (if applicable).
• Any dependent changes have been merged and published in downstream modules.

[coderabbitai]

Important

Review skipped

Auto reviews are disabled on base/target branches other than the default branch.

🗂️ Base branches to auto review (2)

• main
• develop

Please check the settings in the CodeRabbit UI or the .coderabbit.yaml file in this repository. To trigger a single review, invoke the @coderabbitai review command.

⚙️ Run configuration

Configuration used: Path: .coderabbit.yaml

Review profile: ASSERTIVE

Plan: Pro

Run ID: c7317879-ad29-4918-a8f5-89e24af444cf

You can disable this status message by setting the reviews.review_status to false in the CodeRabbit configuration file.

Use the checkbox below for a quick retry:

• 🔍 Trigger review

✨ Finishing Touches

🧪 Generate unit tests (beta)

• Create PR with unit tests

---

Thanks for using CodeRabbit! It's free for OSS, and your support helps us grow. If you like it, consider giving us a shout-out.

❤️ Share

• X
• Mastodon
• Reddit
• LinkedIn

_{Comment @coderabbitai help to get the list of available commands and usage tips.}

[github-actions]

⚠️ This PR has merge conflicts.

Please resolve the merge conflicts before review.

Your PR will only be reviewed by a maintainer after all conflicts have been resolved.

📺 Watch this video to understand why conflicts occur and how to resolve them:
https://www.youtube.com/watch?v=Sqsz1-o7nXk