Desktop app sidebar should show all local sessions from ~/.claude/projects/, not just sessions started in the app

Title: Desktop app sidebar should show all local sessions from ~/.claude/projects/, not just sessions started in the app

Body:

Is your feature request related to a problem? Please describe.
The terminal CLI's resume picker (claude -r) lists every local session transcript stored under ~/.claude/projects/<project>/, across all projects — in my case, 37 sessions. The desktop app's session sidebar only shows sessions that were started from within the desktop app itself (2, in my case), even though the underlying transcript files for all 37 already exist locally on disk and are readable by the same account/user.

Describe the solution you'd like
Have the desktop app scan ~/.claude/projects/ (the same source claude -r reads from) and surface all local session transcripts in the sidebar, not just the ones initiated inside the app. Since the data is already local, this shouldn't require any new sync/import mechanism — just reading the same files the CLI already uses.

Describe alternatives you've considered
Browser extensions like "Attic" do something similar for claude.ai by manipulating the web page directly, but there's no equivalent hook for the desktop app to read/display sessions initiated elsewhere (e.g. from the terminal).

Additional context
This would make the desktop app and CLI feel like one continuous tool rather than two separate session histories on the same machine.