Add filters for journalctl and fs_cli (systemd/FreeSWITCH dev workflows)

Summary

Requesting RTK filter support for two commands that show up heavily in systemd-service and FreeSWITCH development workflows but currently pass through unfiltered: journalctl and fs_cli.

From rtk discover on a real project (34 sessions, 2880 Bash commands), these were among the top unhandled commands:

• journalctl — 32 invocations (e.g. journalctl -u portal-backend -u portal-frontend)
• fs_cli — 29 invocations (e.g. sudo /usr/local/freeswitch/bin/fs_cli -x "sofia status")

Both produce verbose output that is a strong fit for RTK-style compression.

journalctl

Why it's noisy: Default output repeats the full timestamp, hostname, unit, and PID on every line; multi-unit tails (-u a -u b) interleave and balloon fast.

Suggested filter behavior:

• Strip the redundant per-line hostname and leading year/timezone from timestamps (keep MMM DD HH:MM:SS).
• Collapse repeated identical log lines into a single line with an (xN) count.
• Respect -n/--lines, -u, -p/--priority, --since, and -o json (pass JSON through untouched).
• Preserve full content under -x / when a single line is an error or stacktrace.

fs_cli

Why it's noisy: FreeSWITCH -x command output (e.g. sofia status, show channels, show registrations) is wide ASCII tables with separator rows and trailing row-count footers.

Suggested filter behavior:

• Drop decorative separator rows (====, ----, +---+).
• Compress show channels/show registrations tables, keeping headers + data rows, dropping the redundant N total. footer when row count is derivable.
• Handle the common invocation shapes: fs_cli -x "<cmd>" and absolute-path binaries like /usr/local/freeswitch/bin/fs_cli.
• Pass through cleanly when output is already small (single OK/error line).

Environment

• rtk 0.42.1, Linux x86_64 (musl build)
• Both commands frequently invoked via sudo and with absolute paths — matcher should handle a sudo prefix and full binary paths.