Implement frontend session routing flow

- Validate and prepare access links in apps/frontend
- Add session, ended, and unauthorized routes with polling
- Copy full public access URLs from the admin links page

apps/frontend/src/routes/session/+page.svelte

@@ -0,0 +1,141 @@
+<script lang="ts">
+    import { goto } from "$app/navigation";
+    import {
+        mapLinkErrorToSessionEndReason,
+        resolveLinkFresh,
+    } from "$lib/domains/link/client";
+    import { onMount } from "svelte";
+
+    const POLL_INTERVAL_MS = 2000;
+    const MAX_CONSECUTIVE_POLL_ERRORS = 3;
+
+    let state: "loading" | "ready" = "loading";
+    let token = "";
+    let streamUrl: string | null = null;
+    let statusText = "Connecting to your active session...";
+
+    onMount(() => {
+        let disposed = false;
+        let timer: ReturnType<typeof setInterval> | null = null;
+        let inFlight = false;
+        let consecutivePollErrors = 0;
+
+        const endSession = async (reason: string) => {
+            if (disposed) return;
+            if (timer) clearInterval(timer);
+            streamUrl = null;
+            await goto(`/session-ended?reason=${encodeURIComponent(reason)}`, {
+                replaceState: true,
+            });
+        };
+
+        const pollValidity = async () => {
+            if (disposed || inFlight || !token) return;
+            inFlight = true;
+
+            try {
+                const result = await resolveLinkFresh(token);
+
+                if (disposed) return;
+
+                if (result?.error || !result?.data) {
+                    await endSession(
+                        mapLinkErrorToSessionEndReason(result?.error),
+                    );
+                    return;
+                }
+
+                consecutivePollErrors = 0;
+
+                if (result.data.link.status !== "active") {
+                    await endSession("expired");
+                    return;
+                }
+
+                const nextStreamUrl = result.data.device.streamUrl;
+                if (typeof nextStreamUrl === "string" && nextStreamUrl.length > 0) {
+                    streamUrl = nextStreamUrl;
+                }
+            } catch {
+                consecutivePollErrors += 1;
+                if (consecutivePollErrors >= MAX_CONSECUTIVE_POLL_ERRORS) {
+                    await endSession("network");
+                }
+            } finally {
+                inFlight = false;
+            }
+        };
+
+        const start = async () => {
+            token =
+                new URLSearchParams(window.location.search)
+                    .get("token")
+                    ?.trim() || "";
+
+            if (!token) {
+                await goto("/unauthorized?reason=missing_token", {
+                    replaceState: true,
+                });
+                return;
+            }
+
+            const initial = await resolveLinkFresh(token);
+            if (initial?.error || !initial?.data) {
+                await endSession(mapLinkErrorToSessionEndReason(initial?.error));
+                return;
+            }
+
+            streamUrl = initial.data.device.streamUrl;
+            state = "ready";
+            statusText = "Session active";
+
+            await pollValidity();
+            timer = setInterval(() => {
+                void pollValidity();
+            }, POLL_INTERVAL_MS);
+        };
+
+        void start();
+
+        return () => {
+            disposed = true;
+            if (timer) clearInterval(timer);
+        };
+    });
+</script>
+
+<main class="bg-background text-foreground min-h-screen">
+    {#if state === "loading"}
+        <section class="flex min-h-screen items-center justify-center px-6">
+            <div
+                class="w-full max-w-sm rounded-xl border border-border bg-card p-6 text-center"
+            >
+                <h1 class="text-xl font-semibold">Loading session</h1>
+                <p class="mt-3 text-sm text-muted-foreground">
+                    {statusText}
+                </p>
+            </div>
+        </section>
+    {:else}
+        <section class="flex min-h-screen flex-col">
+            <div class="flex items-center justify-center border-b border-border px-3 py-2">
+                <p class="text-xs text-muted-foreground">{statusText}</p>
+            </div>
+            <div class="bg-black flex-1">
+                {#if streamUrl}
+                    <iframe
+                        src={streamUrl}
+                        title="Android session"
+                        class="h-full w-full border-0"
+                        allow="autoplay; fullscreen"
+                        referrerpolicy="no-referrer"
+                    ></iframe>
+                {:else}
+                    <div class="flex h-full items-center justify-center">
+                        <p class="text-sm text-white/70">Waiting for stream...</p>
+                    </div>
+                {/if}
+            </div>
+        </section>
+    {/if}
+</main>