[Feature Request] Sidebar: nest sub-folders within the same Git repo as separate project blocks

Summary

Allow the desktop app's sidebar to treat sub-folders within the same Git repository as distinct project blocks, organized in a hierarchy.

Current behavior

• When two projects live in different Git repositories, they appear as separate blocks in the sidebar — great.
• When two projects live in different sub-folders of the same Git repository (e.g. a monorepo), they are collapsed into a single block keyed by the repository root.
• As a result, sessions started in different sub-folders all stack under the top-level repo entry, and it becomes hard to tell which sub-folder a session belongs to.

Expected behavior

• Sub-folders within the same repo should be shown as nested entries under the repository block (or as their own blocks), so each sub-folder can be managed as its own project.
• Selecting a nested sub-folder should keep its sessions grouped under that sub-folder, not merged into the repo-root block.

Use case

• Monorepos that contain multiple independent projects (apps, packages, business domains) under one Git repo.
• Large internal repos where multiple areas are worked on in parallel and need to be tracked separately in the session history.

Notes

• Repo-level grouping is still useful as the parent — the request is to add a level of hierarchy underneath, not to remove the repo grouping.

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（日本語）同じGitリポジトリ内のサブフォルダも、別リポジトリと同じようにサイドバーで階層的に分けて、フォルダごとにプロジェクト管理できるようにしてほしいという要望です。モノリポ構成で複数プロジェクトを管理しているケースを想定しています。