Resync steering on listener state changes

[kacy]

Summary

• resync VIP steering when the L7 listener starts, stops, or fails its accept loop
• register the listener state-change hook from server and local deploy startup
• add a steering regression covering listener-driven mapping apply and removal

Validation

• zig fmt on touched files
• timeout 45 env YOQ_SKIP_SLOW_TESTS=1 ZIG_GLOBAL_CACHE_DIR=.zig-global-cache ZIG_LOCAL_CACHE_DIR=.zig-local-cache zig build test -Doptimize=ReleaseSafe -- --test-filter "listener state changes resync steering"
• timeout 45 env YOQ_SKIP_SLOW_TESTS=1 ZIG_GLOBAL_CACHE_DIR=.zig-global-cache ZIG_LOCAL_CACHE_DIR=.zig-local-cache zig build