refactor(app_api): extract cli_bridge wrappers into own submodule

Lift the four cli_publish_* Tauri commands (player_snapshot,
library_list, server_list, search_results) out of app_api/core.rs
into app_api/cli_bridge.rs. Each is a thin pass-through to
`crate::cli::write_*_response` — the renderer-side counterpart to the
file-based IPC layer in cli/exchange.rs.

This is the "cli-bridge" slice from cucadmuh's plan for splitting
core.rs's mixed concerns. Together with the earlier perf split,
core.rs is now down to runtime-control + platform + logging slices —
one possible follow-up but each is small enough to leave as-is for now.

app_api/core.rs: 122 → 99 LOC.

src-tauri/src/lib_commands/app_api/mod.rs

@@ -1,5 +1,6 @@
 use super::*;
 
+mod cli_bridge;
 mod core;
 mod navidrome;
 mod perf;
@@ -7,6 +8,7 @@ mod remote;
 mod integration;
 mod analysis;
 
+pub(crate) use cli_bridge::*;
 pub(crate) use core::*;
 pub(crate) use navidrome::*;
 pub(crate) use perf::*;