refactor(ps): move pr_status computation to daemon

[proboscis]

Summary

• Add PRStatus enum and field to proto Run message
• Daemon now computes pr_status from run data and branch state
• CLI uses daemon-provided pr_status instead of computing locally
• Remove prStatusFromRun() and branchStatusFromGitState() functions

Changes

Proto (api/orch.proto)

• Added PRStatus enum: NONE, OPEN, MERGED, CLOSED
• Added pr_status field (field 20) to Run message

Daemon

• proto_handler.go: Added computePRStatus() function
• proto_client.go: Added protoPRStatusToString() conversion
• types.go: Added PRStatus field to RunSummary and RunFull

CLI (internal/cli/ps.go)

• Removed prStatusFromRun() function
• Removed branchStatusFromGitState() function
• Uses daemon-provided PRStatus directly from orchapi.Run

Tests

• Removed TestPrStatusFromRun and TestBranchStatusFromGitState tests
• Updated remaining tests to provide mock prStatusByRun values

Testing

go test ./internal/...   # All pass
go build ./...           # Clean build

Closes: orch-387