fix: honor Reduce Motion and Reduce Transparency

[melonamin]

Summary

• observe macOS accessibility display-option changes and reapply AppKit window/sidebar state live
• suppress repeating sidebar and dashboard status animations when Reduce Motion is enabled
• force opaque windows, command palettes, and session switchers when Reduce Transparency is enabled
• preserve the user's saved opacity and blur values while the system override is active

Why

Status animations repeated indefinitely regardless of Reduce Motion, and translucent window/panel backgrounds remained visible with Reduce Transparency enabled. The app also had no bridge from NSWorkspace.accessibilityDisplayOptionsDidChangeNotification to its AppKit-managed UI.

Validation

• make build
• swift test --package-path agtermCore --skip-build (1,441 tests)
• strict SwiftLint on all changed Swift files
• focused Settings, Dashboard, and sidebar-status UI tests (3 tests)
• manual live-toggle test plan for Reduce Motion and Reduce Transparency

[umputun]

one minor docs issue:

agterm/Views/WindowAppearance.swift:26-29, README.md:146,176,453, .claude/rules/settings.md:177-202, .claude/rules/notifications.md:152-159, the site mirrors, and agterm/Resources/agent-skill/reference.md still describe unconditional blinking and translucency. Please document that Reduce Motion suppresses status animation and Reduce Transparency temporarily forces opaque, unblurred presentation while preserving the saved opacity and blur. The subsystem docs should also include the new .agtermAccessibilityDisplayOptionsChanged live-update path, with the generated site pages kept in sync.