[FEATURE] Group/categorize Projects (folders or tags) to manage many parallel Projects

Preflight Checklist

• [x] I have searched existing requests and this feature hasn't been requested yet
• [x] This is a single feature request (not multiple features)

Problem Statement

Many users run several Projects in parallel — across work, business, and personal contexts (e.g., different clients, initiatives, or personal learning tracks) — each scoped with its own files and instructions. As the number of Projects grows, the flat sidebar list becomes hard to navigate, and related Projects get lost among unrelated ones.

The current workaround is a naming convention (e.g., consistent prefixes), which helps with alphabetical sorting but doesn't provide real grouping, collapsing, or a "category" view.

Proposed Solution

Add a lightweight way to group Projects, such as:

A "Category" or "Folder" field on each Project (optional, user-defined)
A sidebar view that groups/collapses Projects under their category
Optionally, a way to view multiple related Projects' knowledge bases together when needed (stretch goal)

This doesn't require full nested subfolders — even a single-level tag/category with sidebar grouping would solve the core problem of Project-list sprawl for anyone managing multiple parallel Projects (work, business, personal, etc.).

Alternative Solutions

Naming prefixes (helps with sorting, not grouping/collapsing)
Consolidating into one large Project per category (loses per-topic focus and knowledge base scoping)

Priority

Medium - Would be very helpful

Feature Category

Interactive mode (TUI)

Use Case Example

Say a user is taking a structured course — for example, an AI Product Management course with several modules (Customer Discovery, Metrics & Analytics, Prioritization, etc.). Each module works best as its own Project, scoped with just that module's notes, slides, and transcripts, so retrieval stays focused. But across 8–10 modules, these Projects clutter the sidebar alongside unrelated work and personal Projects.

With category/folder grouping, all module Projects (e.g., AIPM-01-CustomerDiscovery, AIPM-02-Metrics, ...) could sit collapsed under one "AI PM Learning" group — while a separate client project or personal to-do Project remains distinct and uncluttered.

Additional Context

_No response_