Add -n/--tail support to lstk logs

[gtsiolis]

Motivation

DevRel parity report: the Python CLI supports localstack logs -n 20 to inspect the last N log lines, while lstk logs only offered all-or-follow — cumbersome on a busy emulator and a migration papercut. -n, --tail (default all) is also the exact convention of docker logs, docker compose logs, and nerdctl logs.

Changes

• Add -n, --tail to lstk logs (string, default "all", wording identical to docker logs); validated at the command boundary — non-negative integer or all
• Thread the value through container.Logs / ui.RunLogs into runtime.StreamLogs, which previously hardcoded Tail: "all"
• --follow --tail N shows the last N lines and then streams (handled natively by the Docker API)
• Regenerate MockRuntime for the StreamLogs signature change

Tail applies to raw log lines before the noise filter (docker semantics), so --tail 20 can display fewer than 20 lines unless -v is passed.

Tests

• New integration tests, red-green verified: --tail/-n limit output, default shows all lines, invalid values are rejected with a helpful error, and --follow --tail starts from the tail
• Manually verified against a real container in both plain and TUI (PTY) modes, including --tail 0, --tail all, over-count values, and combined -fn 3

Closes PRO-358