feat(tui): replace legacy terminal UI with OpenTUI

[JSONbored]

Summary

• replace the in-process Go Bubble Tea TUI with an OpenTUI sidecar launched by the Go scanner engine
• keep Nightward's core scanner/report/policy logic in Go while shipping nightward-tui beside nightward and nw
• tighten Raycast findings, provider doctor, and menu-bar status surfaces so they are less crowded and more useful
• regenerate fixture-only OpenTUI GIF/PNG assets and update README/site/docs to match the shipped interface

What changed

• added packages/tui with OpenTUI/Bun source, model tests, demo command, and sidecar build scripts
• rewired internal/tui to write a private redacted review bundle and launch nightward-tui
• removed Bubble Tea/Bubbles/Lip Gloss Go dependencies and legacy VHS media
• added GoReleaser sidecar packaging for macOS/Linux arm64/amd64 and Windows amd64, with archive smoke coverage for the sidecar
• narrowed npm launcher/docs away from Windows ARM64 until the OpenTUI sidecar has a supported compile target
• improved Raycast provider install actions with confirmation, severity-grouped findings, and a compact menu-bar dropdown

Why

• Nightward is still new enough to replace the TUI cleanly without preserving a legacy UI surface
• OpenTUI gives the project a better visual ceiling while keeping the single-command install story through release sidecars
• Raycast needed a cleaner Beszel-style information hierarchy and actual provider install affordances instead of copy-only actions

Validation

• make verify
• make release-snapshot
• make opentui-demo
• make install-local
• inspected snapshot archives and confirmed Unix archives include nightward-tui and Windows archives include nightward-tui.exe
• installed local nightward, nw, and nightward-tui into ~/.local/bin; nightward --version and nw --version report 0.1.5-0.20260502081248-2d473d61f39d

Notes

• Release snapshot currently emits five archives: darwin/linux arm64/amd64 and windows amd64. Windows ARM64 is intentionally deferred because Bun 1.2.21 does not support the required OpenTUI sidecar compile target.
• Raycast Store submission still needs fixture-only metadata screenshots and manual ray develop evidence before a store PR.