TUI: add profile management modal

[rmanibus]

Summary

• replace prompt-based profile management with a real in-TUI modal for create, edit, and delete
• add smarter source entry with source type plus type-specific details and provider-aware auth selection
• improve modal UX with aligned fields, required markers, inline examples, validation highlighting, and immediate Esc cancel

Closes #221

Verification

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

[codecov]

Codecov Report

❌ Patch coverage is 49.40653% with 341 lines in your changes missing coverage. Please review.

Files with missing lines	Patch %	Lines
cmd/cloudstic/cmd_tui_profile_form.go	44.07%	233 Missing and 36 partials ⚠️
internal/tui/shell.go	68.34%	30 Missing and 14 partials ⚠️
cmd/cloudstic/tui_runtime.go	39.13%	10 Missing and 4 partials ⚠️
internal/app/tui_service.go	44.00%	7 Missing and 7 partials ⚠️

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