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.

.github/workflows/ci.yml

@@ -107,3 +107,13 @@ jobs:
         env:
           SOULSEEK_E2E_REQUIRED: "1"
         run: cargo test -p soulseek-rs --test cli_e2e -- --nocapture
+
+      # The same suite again, with every session served by a daemon instead of
+      # the command's own login. Identical records and exit codes both ways is
+      # what makes daemon mode a routing decision rather than a second
+      # implementation to keep in step.
+      - name: Run CLI e2e tests against a daemon
+        env:
+          SOULSEEK_E2E_REQUIRED: "1"
+          SOULSEEK_E2E_MODE: daemon
+        run: cargo test -p soulseek-rs --test cli_e2e -- --nocapture --test-threads=1