TUI: add per-profile backup history view

[rmanibus]

Summary

• add summary/history subviews to the selected profile pane in the TUI
• show recent snapshots for the selected profile with time and snapshot ref
• preserve the selected history view across dashboard refreshes and add test coverage for the new shortcuts/state

Closes #222

Verification

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

[codecov]

Codecov Report

❌ Patch coverage is 84.78261% with 14 lines in your changes missing coverage. Please review.

Files with missing lines	Patch %	Lines
internal/tui/dashboard.go	81.08%	4 Missing and 3 partials ⚠️
internal/tui/shell.go	83.72%	4 Missing and 3 partials ⚠️

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