init: transfer thinking level menu to messageinput.svelte

[Yeetster-cmd]

Pull Request Checklist

Before submitting, make sure you've checked the following:

• Description: Provide a concise description of the changes made in this pull request down below.
• Changelog: Ensure a changelog entry following the format of Keep a Changelog is added at the bottom of the PR description.
• Dependencies: Are there any new or upgraded dependencies? If so, explain why, update the changelog/docs, and include any compatibility notes. Actually run the code/function that uses updated library to ensure it doesn't crash.
• Testing: Perform manual tests to verify the implemented fix/feature works as intended AND does not break any other functionality. Include reproducible steps to demonstrate the issue before the fix. Test edge cases (URL encoding, HTML entities, types). Take this as an opportunity to make screenshots of the feature/fix and include them in the PR description.
• Agentic AI Code: Confirm this Pull Request is not written by any AI Agent or has at least gone through additional human review AND manual testing. If any AI Agent is the co-author of this PR, it may lead to immediate closure of the PR.
• Code review: Have you performed a self-review of your code, addressing any coding standard issues and ensuring adherence to the project's coding standards?
• Design & Architecture: Prefer smart defaults over adding new settings; use local state for ephemeral UI logic. Open a Discussion for major architectural or UX changes.
• Git Hygiene: Keep PRs atomic (one logical change). Clean up commits and rebase on dev to ensure no unrelated commits (e.g. from main) are included. Push updates to the existing PR branch instead of closing and reopening.

Changelog Entry

Description

• [Concisely describe the changes made in this pull request, including any relevant motivation and impact (e.g., fixing a bug, adding a feature, or improving performance)]

Added

• [List any new features, functionalities, or additions]

Changed

• [List any changes, updates, refactorings, or optimizations]

Deprecated

• [List any deprecated functionality or features that have been removed]

Removed

• [List any removed features, files, or functionalities]

Fixed

• [List any fixes, corrections, or bug fixes]

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Additional Information

• [Insert any additional context, notes, or explanations for the changes]
  • [Reference any related issues, commits, or other relevant information]