fix(git): preserve trailing newline on status --short/--porcelain (#3303)

[NanoRisk6]

What Problem This Solves

rtk git status --short / --porcelain filtered output was emitted with print! after join("\n"), so the final entry had no trailing newline. That breaks while read loops and glues the last line to following output. Fixes #3303.

Why This Change Was Made

Print status output with a trailing newline when the filtered file list is non-empty, matching native git status --short / --porcelain behavior.

User Impact

Scripts and agent parsers that read status line-by-line work correctly again.

Evidence

• Focused unit/integration coverage for short/porcelain trailing newline.
• Local cargo test for the status filter path.

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