Strengthen TUI edge-case coverage

[rmanibus]

Summary

• add focused TUI runtime tests for refresh failure and live redraw width polling
• add narrow-width and layout coverage for the TUI renderer
• fix suspended raw-mode restoration and footer truncation on narrow terminals

Testing

• env GOCACHE=/tmp/cloudstic-gocache go test -count=1 ./cmd/cloudstic ./internal/tui
• env GOCACHE=/tmp/cloudstic-gocache GOLANGCI_LINT_CACHE=/tmp/cloudstic-golangci-lint golangci-lint run ./cmd/cloudstic ./internal/tui
• env GOCACHE=/tmp/cloudstic-gocache go test -count=1 -cover ./cmd/cloudstic
• env GOCACHE=/tmp/cloudstic-gocache go test -count=1 -cover ./internal/tui

Closes #219

[codecov]

Codecov Report

❌ Patch coverage is 68.00000% with 8 lines in your changes missing coverage. Please review.

Files with missing lines	Patch %	Lines
cmd/cloudstic/tui_runtime.go	61.90%	5 Missing and 3 partials ⚠️

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