Improve TUI activity panel and progress

[rmanibus]

Summary

• replace the raw activity log slice with a structured TUI activity panel
• preserve activity state across dashboard refreshes and show last action metadata
• add a native TUI progress bar for phases with known totals

Testing

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

Closes #216

[codecov]

Codecov Report

❌ Patch coverage is 61.53846% with 45 lines in your changes missing coverage. Please review.

Files with missing lines	Patch %	Lines
internal/tui/shell.go	63.07%	18 Missing and 6 partials ⚠️
cmd/cloudstic/cmd_tui_activity.go	58.00%	18 Missing and 3 partials ⚠️

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