fix(tui): detail panel loading, overlay drift; add theme selector

[chxmxii]

Bug fixes

• Detail panel stuck on "… loading": pressing 1/2/3 set the loading state but no debug command was ever dispatched, and debugOutputMsg was only routed to the overlay. The root model now issues the command and routes tagged results back to the detail panel, dropping stale responses if the tab changed mid-flight.
• Refresh reset the detail tab: every poll tick re-set the container, snapping the panel back to the info view and wiping content. Same-container updates now preserve the active tab, content, and scroll.
• Overlay text crawling out of the box: View() mutated the stored content lines in place, prepending one space per render. Rendering now builds a fresh slice and is idempotent (regression test added).
• Tabs/CR escaping panel borders: FitCol/ClipLine now strip \r and expand tabs to 8-column stops, so raw inspect/top/netstat output can't move the cursor past the border.

Theme selector

• Five built-in adaptive themes: catppuccin (default), dracula, nord, gruvbox, tokyo-night.
• T in the dashboard opens a live-preview picker (↑↓ preview, Enter applies + persists to ~/.config/containershell/theme, Esc reverts).
• containershell dashboard --theme <name> overrides per run; saved preference is loaded for all TUI surfaces.
• Styles are read from pkg/tui at render time instead of init-time copies, so switches apply instantly.

Verification

• go build, go vet, go test -race ./... all green (new unit tests for dispatch/routing, overlay idempotency, tab expansion, theme registry).
• Live E2E against rootless Podman 5.8.4 via tmux: env/top tabs load real data and survive refresh ticks; inspect overlay pixel-identical across 11s of renders; theme picker previews, applies, persists across restart, and Esc reverts.

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