fix(notifications): resolve an item's relative url, and document the CI trigger

Two things the live rig found, and the README half of the trigger change.

Phase 7 specifies an inbox item's `url` is RELATIVE-ONLY and validates it as
such — right for a browser already on the site, a dead link on a phone. The
first cut here only opened `http(s)`-prefixed strings, so on the rig every link
in the inbox did nothing at all. `InboxViewModel.linkFor` now resolves against
the configured base with OkHttp's `HttpUrl.resolve`, which absolutises the path
and returns null for anything that would not end up http(s) — so a `javascript:`
or `intent:` url in a notification body opens nothing.

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

app/src/main/java/com/runicgateway/app/ui/notifications/InboxScreen.kt

@@ -118,11 +118,11 @@ fun InboxScreen(
                     onEndReached = viewModel::loadMore,
                     onOpen = { item ->
                         viewModel.markRead(item.id)
-                        // The url is the site's own page for the item, and most items
-                        // have none — an inbox row is complete on its own. Anything
-                        // that is not http(s) is not opened at all.
-                        item.url?.takeIf { it.startsWith("http://") || it.startsWith("https://") }
-                            ?.let { WebHandoff.open(context, it) }
+                        // Most items have no url at all — an inbox row is complete on
+                        // its own — and the ones that do carry a SITE-RELATIVE path,
+                        // so the view model resolves it against the configured shard
+                        // before anything is opened.
+                        viewModel.linkFor(item)?.let { WebHandoff.open(context, it) }
                     },
                 )
             }

app/src/main/java/com/runicgateway/app/ui/notifications/InboxViewModel.kt

@@ -201,6 +201,25 @@ class InboxViewModel @Inject constructor(
         cacheCurrent()
     }
 
+    /**
+     * The absolute link for an item, or null when it has none this app can open.
+     *
+     * **An item's `url` is SITE-RELATIVE** — `/guilds/the-silver-anvil/forum/403`
+     * is what the server writes, because it is rendered from the template's button
+     * block for a browser that is already on the site. A phone is not, so it has to
+     * be resolved against the configured base or every link in the inbox is dead;
+     * the live rig is what caught that.
+     *
+     * `HttpUrl.resolve` does both jobs: it absolutises a relative path and it
+     * returns null for anything that would not end up as http(s) — a `javascript:`
+     * or `intent:` url in a notification body opens nothing at all.
+     */
+    fun linkFor(item: NotificationItemDto): String? {
+        val raw = item.url?.trim().orEmpty()
+        if (raw.isEmpty()) return null
+        return baseUrlHolder.current?.resolve(raw)?.toString()
+    }
+
     /**
      * Keep the snapshot in step with a local read.
      *

app/src/test/java/com/runicgateway/app/ui/notifications/InboxViewModelTest.kt

@@ -166,4 +166,31 @@ class InboxViewModelTest {
         // bring the badge back on the next cold open.
         assertEquals(writesAfterLoad + 1, cache.writes)
     }
+
+    // ── The item link (found by the live rig, not by a test) ──────────────
+
+    @Test fun aSiteRelativeUrlIsResolvedAgainstTheShard() {
+        // What the server actually writes: the template's button block renders a
+        // path, because on the web the reader is already on the site.
+        val vm = viewModel()
+        val item = item(1).copy(url = "/guilds/the-silver-anvil/forum/403")
+        assertEquals("https://shard.example/guilds/the-silver-anvil/forum/403", vm.linkFor(item))
+    }
+
+    @Test fun anAbsoluteUrlIsLeftAlone() {
+        val vm = viewModel()
+        assertEquals("https://elsewhere.example/x", vm.linkFor(item(1).copy(url = "https://elsewhere.example/x")))
+    }
+
+    @Test fun anItemWithNoUrlHasNoLink() {
+        val vm = viewModel()
+        assertNull(vm.linkFor(item(1)))
+        assertNull(vm.linkFor(item(1).copy(url = "   ")))
+    }
+
+    @Test fun aUrlThatCouldNotBeOpenedSafelyResolvesToNothing() {
+        val vm = viewModel()
+        assertNull(vm.linkFor(item(1).copy(url = "javascript:alert(1)")))
+        assertNull(vm.linkFor(item(1).copy(url = "intent://evil#Intent;end")))
+    }
 }