Add `gh search` subcommand support

[mkbctrl]

Problem

gh search subcommands (gh search repos, gh search issues, gh search prs) are not covered by RTK's compression patterns. We observed 35 passthrough invocations in a single audit window.

Affected Commands

Command	Use Case	Frequency
gh search repos	Find repositories by topic/language	~12
gh search issues	Search issues across repos	~15
gh search prs	Search pull requests	~8

Context

gh commands like gh pr view, gh issue view, and gh api may already have patterns, but the search subcommand family produces verbose tabular output that is highly compressible (repeated column headers, long URLs, timestamps).

Expected Behavior

Compress search result tables to essential columns (title, number, state, URL) and truncate long result sets.

Environment

• RTK v0.27.2
• gh CLI 2.x

[pszymkowiak]

Fixed in v0.30.0 — gh search works via passthrough. Tested locally: rtk gh search repos "rtk" --limit 2 returns results correctly.