feat(statusline): lower max rigs to 3 and add alias support

- Add Alias field to RigEntry struct for short display names
- Limit displayed rigs to 3 (was unlimited, causing overflow)
- Use alias in statusline when configured (e.g., gcr instead of google_cookie_retrieval)
- Show +N overflow indicator when more rigs exist

Closes: hq-5j33zz

internal/config/types.go

@@ -168,6 +168,7 @@ type RigEntry struct {
 	AddedAt     time.Time           `json:"added_at"`
 	BeadsConfig *BeadsConfig        `json:"beads,omitempty"`
 	Crew        *CrewRegistryConfig `json:"crew,omitempty"`
+	Alias       string              `json:"alias,omitempty"` // Short display name for statusline
 }
 
 // BeadsConfig represents beads configuration for a rig.