fix: prevent black Metal terminal frames

[batonogov]

Summary

• route terminal recovery redraws through the renderer that owns the pixels
• invalidate SwiftTerm Metal row caches and its nested on-demand MTKView
• retry the first frame at four bounded intervals after every view attachment
• cancel pending retries on detach and preserve the CoreGraphics fallback
• log Metal initialization failures instead of silently swallowing them
• cover initial attachment, detach, same-window reattachment, and backend routing

Root cause

With Metal enabled, SwiftTerm returns early from the outer LocalProcessTerminalView draw path because a nested MTKView owns presentation. Pine still called setNeedsDisplay and displayIfNeeded on the outer view, so recovery redraws could be no-ops. A freshly attached CAMetalLayer may also temporarily have no currentDrawable; SwiftTerm records the missed frame, but that state is only consumed after a successful command buffer completes.

The compatibility bridge uses public SwiftTerm 1.14 APIs: selectionChanged(source:) marks the visible Metal range dirty, while a same-size setFrameSize(_:) immediately reaches SwiftTerm internal Metal display request without changing the PTY geometry.

Testing

• SwiftLint 0.65.0 on all changed Swift files: 0 violations
• Swift 6.4 syntax parsing and targeted type checking
• reentrancy guard for Pine sources
• standalone runtime check on the host Metal device confirmed that the backend-aware request invalidates the nested MTKView
• full xcodebuild test suite was not run locally because /Applications/Xcode.app is unavailable; CI should run the complete suite

Fixes #1128