FIX: make terminal backgrounds consistent and approval buttons visible

[merefield]

Apple Terminal could show patches of the profile background inside themed panels and buttons: nested text styles reset the background, borders used a separate default background, and unused screen cells retained the Terminal profile colour. These changes paint the intended theme backgrounds explicitly and give approval decisions solid, high-contrast fills.

• Fill default-background cells while preserving explicit editor tints, highlights, text attributes and hyperlinks; reset styling at component boundaries.
• Paint the full alternate-screen canvas and panel/button borders consistently. Inline mode remains bounded to its rendered content, and the Terminal profile is not modified.
• Recognise local Apple Terminal true-colour support on macOS Tahoe (26) and newer. Respect explicit colour preferences and retain normal detection for older, remote and multiplexed terminals. Windows colour detection is unchanged.
• Make approval decision buttons visible before hover, with distinct armed-confirmation and hover colours. Keep decision routing, confirmation requirements and hit targets intact.
• Add cell-colour, contrast, geometry, inline-mode and capability-detection regressions; update the rendering snapshot and troubleshooting guidance.

The shared background fills and approval-button styling also change Windows appearance. Native Windows Terminal visual verification is still pending; font-dependent box-character seams may still vary.

Validation completed on macOS:

• Core suite: go test -race -cover -timeout 10m -skip '^TestLocalisedScreens$' ./...
• All 17 locale options: go test -race -cover -timeout 10m -run '^TestLocalisedScreens$' ./internal/ui
• go vet ./..., formatting and git diff --check
• make build and local binary version smoke check
• Windows amd64 cross-compilation of both the application and UI test executable; these were not executed on Windows.

Windows visual check before merge: build this branch, compare all themes and normal/hover/pressed button states, open an approval pill to inspect decision controls, and check editor/queue tints, resizing and inline rendering.

[Copilot]

🟡 Changes recommended

Treat an empty NO_COLOR value as an explicit opt-out.

1 open finding

• Respect empty NO_COLOR values as a true-colour opt-out · New

What changed in this PR

This PR standardizes terminal backgrounds, improves approval-button visibility, and adds Apple Terminal true-colour detection.

Changes:

• Adds explicit backgrounds across canvases, panels, editors, borders, and buttons.
• Adds approval-control styling and rendering regressions.
• Adds macOS Tahoe capability detection and documentation.
• Requires handling empty NO_COLOR values as an opt-out.

File	Summary
README.md	Updates rendering and troubleshooting guidance.
main.go	Applies terminal-specific options.
main_terminal.go	Detects Apple Terminal true-colour support.
main_terminal_test.go	Tests capability detection.
main_terminal_other.go	Provides non-macOS fallback.
main_terminal_darwin.go	Detects supported macOS versions.
internal/​ui/​view.go	Paints canvas and panel backgrounds.
internal/​ui/​monitor.go	Applies button backgrounds.
internal/​ui/​monitor_suggestions.go	Paints suggestion-popup borders.
internal/​ui/​monitor_editor.go	Preserves editor tint backgrounds.
internal/​ui/​monitor_approval.go	Styles approval decision controls.
internal/​ui/​english_snapshot_test.go	Updates rendering snapshots.
internal/​ui/​background.go	Implements background filling.
internal/​ui/​background_test.go	Adds background and rendering regressions.
go.mod	Promotes rendering dependencies to direct requirements.

🧠 Review effort: Lite

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