Add a results archive and purge orphaned passing rows on delete

Until now there was no way to find a completed session without already
knowing which event it belonged to - navigation was strictly Events ->
one event -> its sessions. A new "Resultatarkiv" view lists every
finished session across all events, searchable by event/session name,
class, driver and date range.

Opening a session reuses the existing single-session leaderboard
builder for standings and the existing per-competitor lap lookup for
lap history - no new results logic - plus a session-wide penalties/
corrections list (resultsBySession[id].adjustments), previously only
visible in the live judging action log. Export buttons reuse the
existing per-event PDF and race-package JSON export functions rather
than adding a new format.

Investigated what should happen to raw timing data when a race is
deleted. Training statistics and session replay already read from
their own independent, deliberately-retained copies that survive
deletion by existing design - unaffected either way. The one thing
that outlived deletion with no purpose was the raw `passings` SQLite
rows (write-only; nothing in the app reads them), growing forever with
driver IDs never purged. A new POST /api/passings/purge endpoint now
removes exactly the deleted session(s)' rows, called as a best-effort
side call from both delete-event and delete-session.

Also fixes a real bug found while building this: ensureSessionResult
guarded adjustments/splits/pitEvents/pitStops against being missing on
an already-existing result, but not passings itself, so viewing lap
history for such a result (e.g. an older/imported race package)
crashed outright.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

tests/server_persistence.integration.test.js

@@ -282,6 +282,34 @@ test("SQLite API persists state, passings, and overlay session results", { timeo
     assert.equal(rowsPayload.rows[0].car_id, "car_1");
     assert.equal(rowsPayload.rows[0].strength, -52.5);
     assert.deepEqual(JSON.parse(rowsPayload.rows[0].raw_json), passing);
+
+    // A second, unrelated session's passing must survive purging session_1's rows.
+    await fetch(`${baseUrl}/api/passings`, {
+      method: "POST",
+      headers: { "Content-Type": "application/json" },
+      body: JSON.stringify({ sessionId: "session_other", passing: { ...passing, timestamp: 18000 } }),
+    });
+    const purgeResponse = await fetch(`${baseUrl}/api/passings/purge`, {
+      method: "POST",
+      headers: { "Content-Type": "application/json" },
+      body: JSON.stringify({ sessionIds: ["session_1"] }),
+    });
+    const purgePayload = await purgeResponse.json();
+    assert.equal(purgeResponse.status, 200);
+    assert.equal(purgePayload.ok, true);
+    assert.equal(purgePayload.deleted, 1);
+
+    const afterPurgeSession1 = await (await fetch(`${baseUrl}/api/passings?sessionId=session_1&limit=10`)).json();
+    assert.equal(afterPurgeSession1.rows.length, 0, "the deleted session's rows are gone");
+    const afterPurgeOtherSession = await (await fetch(`${baseUrl}/api/passings?sessionId=session_other&limit=10`)).json();
+    assert.equal(afterPurgeOtherSession.rows.length, 1, "an unrelated session's rows must be untouched");
+
+    const emptyPurgeResponse = await fetch(`${baseUrl}/api/passings/purge`, {
+      method: "POST",
+      headers: { "Content-Type": "application/json" },
+      body: JSON.stringify({ sessionIds: [] }),
+    });
+    assert.deepEqual(await emptyPurgeResponse.json(), { ok: true, deleted: 0 });
   } finally {
     await stopServer(child);
     rmSync(dataDir, { recursive: true, force: true });