refactor: remove dead install progress streaming

[fullstackjam]

What does this PR do?

Removes the obsolete install-progress event bridge and makes the existing linear console progress path unconditional.

Why?

The v5 wizard install screen was intentionally removed in #150, leaving internal/progress, the brew/npm SetProgressSink hooks, and every progressSink.Emit branch without a production caller. The informational deadcode job reports the drift but does not block merges.

Testing

• go vet ./... passes
• Relevant tests added or updated — obsolete streaming-only tests were removed; brew, npm, installer, and archtest packages pass
• Interactive dry-run not run — this removes an unreachable TUI path and preserves the existing linear console behavior

Cross-repo checklist

• No docs/content update is needed in openboot.dev
• No CLI ↔ server API contract change

Notes for reviewer

The no-direct-exec baseline only changes because deleting branches moved two existing, intentional call sites to new line numbers.