test(daemon): drive the whole CLI suite against a daemon, and fix what it caught

SOULSEEK_E2E_MODE=daemon makes the existing e2e harness serve every session
from a daemon instead of the command's own login, so the same 83 tests assert
the same records and exit codes both ways. CI runs the suite twice.

Two defects it found:

serve judged whether anything was shared from this run's configuration
rather than from the session, so routed to a daemon it would start with
nothing to serve and report success.

The TUI showed an empty conversation when attached, because the daemon's
message history was never asked for. It is now a SessionApi method, empty
locally, which puts the difference behind the seam.

main.rs is now a thin entry point over the library rather than a second copy
of every module, so the program compiles once instead of twice.

soulseek-rs/src/directories.rs

@@ -37,6 +37,7 @@ pub fn resolve_shared_directory(
 
 /// Validate several configured share paths; invalid ones are skipped with a
 /// warning instead of aborting (the client just shares less).
+#[cfg_attr(not(test), allow(dead_code))]
 #[must_use]
 pub fn resolve_shared_directories(dirs: &[String]) -> Vec<String> {
     let mut resolved = Vec::new();