Add first interactive TUI dashboard slice

[rmanibus]

Summary

• add a first 'cloudstic tui' command with an interactive terminal dashboard
• show profile/store/auth overview, selected profile details, and an in-TUI activity panel
• support keyboard navigation, resize handling, alternate-screen lifecycle, and context-sensitive init/backup action

Testing

• env GOCACHE=/tmp/cloudstic-gocache go test -count=1 ./internal/status ./internal/app -run 'TestBuildDashboard'
• env GOCACHE=/tmp/cloudstic-gocache go test -count=1 ./internal/tui ./cmd/cloudstic -run 'TestRenderDashboard|TestRunTUI|TestReadTUIAction'
• env GOCACHE=/tmp/cloudstic-gocache go test -count=1 ./e2e -run '^TestCLI_Feature_TUI_'

Follow-up

• Related to RFC 0012: Epic / Tracking issue for interactive TUI mode #132
• Follow-up interaction work is tracked in Implement first interactive TUI dashboard slice #211
• Formal GitHub sub-issue linking for Implement first interactive TUI dashboard slice #211 under RFC 0012: Epic / Tracking issue for interactive TUI mode #132 could not be created with the current token permissions

[codecov]

Codecov Report

❌ Patch coverage is 54.01130% with 407 lines in your changes missing coverage. Please review.

Files with missing lines	Patch %	Lines
internal/tui/shell.go	54.05%	95 Missing and 24 partials ⚠️
cmd/cloudstic/tui_runtime.go	43.18%	84 Missing and 16 partials ⚠️
cmd/cloudstic/cmd_tui_activity.go	50.34%	60 Missing and 11 partials ⚠️
internal/tui/dashboard.go	52.66%	56 Missing and 15 partials ⚠️
cmd/cloudstic/cmd_tui_input.go	60.82%	26 Missing and 12 partials ⚠️
cmd/cloudstic/cmd_tui.go	86.20%	2 Missing and 2 partials ⚠️
cmd/cloudstic/interactive.go	71.42%	1 Missing and 1 partial ⚠️
cmd/cloudstic/store.go	81.81%	1 Missing and 1 partial ⚠️

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