[FEATURE] Desktop app: filter/group sessions by the repo(s) a session worked in

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

In the desktop app sidebar, sessions from all projects and repos are interleaved in one list. When I want to find "that session where I worked on repo X", there's no way to narrow the list down — I have to recognize it by title alone. Sessions also don't visibly indicate which repo/directory they ran in, and a single session sometimes touches more than one repo (worktrees, sibling checkouts), so even remembering the launch directory isn't always enough.

Proposed Solution

Let me filter and/or group the session list by repository / project directory:

• A filter control (dropdown or search token like repo:contracts) that narrows the sidebar to sessions associated with a given repo.
• An optional "group by repo" view mode that clusters sessions under their repo heading.
• Association should be the session's working directory by default, ideally enriched with repos the session actually touched via file/git operations — with the primary repo (most activity) used for grouping when several were involved.
• Showing the repo name as a small badge on each session row would help even without filtering.

Alternative Solutions

Currently I encode the project into session titles manually, or rely on memory of when I ran something. The CLI's claude --resume is implicitly scoped to the current directory, which is exactly the affordance the desktop sidebar lacks.

Priority

Medium - Would be very helpful

Feature Category

Interactive mode (TUI)

Use Case Example

1. I work across several repos in parallel (a contracts repo, a backend repo, a docs/business folder).
2. A week later I need to revisit how a change in the contracts repo was made.
3. With this feature I'd filter the sidebar to contracts and immediately see only the handful of relevant sessions.
4. Today I scroll the full mixed list and guess from titles.

Additional Context

Complements #66974 (user-defined manual groups/colors): that one is about manual organization; this one is about automatic, metadata-driven filtering the app can derive on its own — the session cwd is already known, so a basic version needs no new data collection.