feat(tui): run the highlighted search again with S

The search list survives a restart, but a restored query was only ever a
reminder: seeing what the network has now meant typing it out again. In
the Searches pane, `S` now re-runs the highlighted query in its place — no
duplicate row, no reordering — cancelling a run still collecting first and
starting the Results display over for what comes back.

The key is listed in the shortcut bar, the `?` overlay, the README and the
website. `start_search` is split into launching a search and showing it,
so both paths share one implementation.

A new `tui_e2e` suite drives the real window over a real session against
soulfind: keys in, a screen out, a sharing peer on the other end. It
restores a query from a previous run's state directory, presses `S`, and
checks the peer's file lands on screen — then again once the query has
been on the wire, proving a repeat is answered and the display does not
stack. To make that possible `MainTui` is exported with `handle_key_event`,
`render`, `poll_session` and a `state()` accessor, and CI runs the suite
with `SOULSEEK_E2E_REQUIRED=1`.

Closes #85

.github/workflows/ci.yml

@@ -110,6 +110,14 @@ jobs:
           SOULSEEK_E2E_REQUIRED: "1"
         run: cargo test -p soulseek-rs --test cli_e2e -- --nocapture
 
+      # The window over a real session: keys in, a screen out, a peer on the
+      # other end. The unit tests drive it against a stand-in session and the
+      # CLI suite never opens it, so this is the only place the two meet.
+      - name: Run TUI e2e tests (required against soulfind)
+        env:
+          SOULSEEK_E2E_REQUIRED: "1"
+        run: cargo test -p soulseek-rs --test tui_e2e -- --nocapture
+
       # The control protocol as a third party meets it: the TCP transport, the
       # token, and the gate. None of it is reachable through the command
       # surface, so the CLI suite cannot cover it in either mode.