fix: run git fetch for all SSH workspaces

[ammar-agent]

Problem

Git fetch was only running once per project per polling cycle. This optimization worked for local workspaces that share a git repository, but broke for SSH workspaces where each workspace has its own independent git repository.

Solution

Changed the fetch key logic to distinguish between local and SSH workspaces:

• Local workspaces: Use projectName as fetch key → one fetch serves all workspaces (efficient)
• SSH workspaces: Use workspaceId as fetch key → each workspace gets its own fetch (correct)

Changes

• Add getFetchKey() to determine fetch key based on runtime type
• Rename tryFetchNextProject → tryFetchWorkspaces
• Rename fetchProject → fetchWorkspace
• Remove groupWorkspacesByProject (no longer needed)

Impact

Before (Bug)

Polling Cycle 1:
  SSH Workspace A (project-x) ───┐
  SSH Workspace B (project-x) ───┼─→ Fetch key: "project-x"
  SSH Workspace C (project-x) ───┘   ❌ Only ONE fetch runs

After (Fixed)

Polling Cycle 1: SSH Workspace A (id: abc123) ──→ Fetch key: "abc123" ✓
Polling Cycle 2: SSH Workspace B (id: def456) ──→ Fetch key: "def456" ✓
Polling Cycle 3: SSH Workspace C (id: ghi789) ──→ Fetch key: "ghi789" ✓

This ensures SSH workspaces get fresh git status updates while maintaining efficient fetch behavior for local workspaces.

Testing

The existing tests in GitStatusStore.test.ts continue to pass. The changes only affect internal fetch scheduling logic and maintain backward compatibility for local workspaces.