Add keybinding to cycle the log tail line count in the Logs tab

[DevLeonardoK]

Description

Adds a t keybinding (available in the containers and services panels) that cycles how many lines are shown in the Logs tab: all → 50 → 100 → 200 → 500 → all. The current value is displayed in the Logs tab subtitle, e.g. tail: 50 (t to cycle).

This builds on the existing logs.tail config option, which now acts as the initial value; the keybinding lets you change it at runtime without editing the config or restarting.

Behavior details

• The tail count is a true sliding window: with tail: 50, the main panel always shows only the 50 most recent lines as new ones stream in, rather than just limiting the initial snapshot and growing unbounded afterwards (which is what a bare docker logs --tail 50 --follow does). This is implemented with a small writer that keeps the last N lines and atomically rewrites the view via SetContent, so there is no empty-frame flicker.
• Works from both the containers panel and the services panel (the services Logs tab renders the underlying container's logs through the same path).
• The tail value is part of the main-panel context cache key, so cycling forces a re-render immediately.
• Viewing logs in a subprocess (m) is unchanged and keeps plain docker logs semantics.

Testing

• go build ./..., go vet ./..., go test ./... all pass; cheatsheets regenerated with go run scripts/cheatsheet/main.go generate.
• Manually verified in a terminal against containers emitting numbered log lines (both a standalone container and a docker-compose service): with tail: 50 the panel shows exactly the 50 most recent lines (e.g. lines 251–300 when the container is at line 300), the window keeps sliding as new lines arrive, and cycling through every preset and back to all behaves as expected.