feat(webapp): give runs a TRIGGER_DASHBOARD_URL environment variable

Runs now get a `TRIGGER_DASHBOARD_URL` environment variable set to the
dashboard's address (`APP_ORIGIN`, without a trailing slash), in dev and
deployed environments. A `TRIGGER_DASHBOARD_URL` set on the project
overrides it. A task can link to its own run on any instance:

```ts
const runUrl = `${process.env.TRIGGER_DASHBOARD_URL}/runs/${ctx.run.id}`;
```

`/runs/<runId>` checks that the viewer belongs to the run's
organization, then redirects to the full run page.

Mono-RevId: 7541a5f02d5c69f77ab422974c9944eac97d722b

Author: ericallam

.server-changes/trigger-dashboard-url.md

@@ -0,0 +1,6 @@
+---
+area: webapp
+type: improvement
+---
+
+Runs now get a `TRIGGER_DASHBOARD_URL` environment variable with the dashboard's address, so a task can link to its run (`${TRIGGER_DASHBOARD_URL}/runs/${ctx.run.id}`) on any Trigger.dev instance. A `TRIGGER_DASHBOARD_URL` you set on the project still wins.

apps/webapp/app/v3/environmentVariables/environmentVariablesRepository.server.ts

@@ -1030,6 +1030,10 @@ async function resolveOverridableTriggerVariables(
       key: "TRIGGER_REALTIME_STREAM_VERSION",
       value: env.REALTIME_STREAM_VERSION,
     },
+    {
+      key: "TRIGGER_DASHBOARD_URL",
+      value: env.APP_ORIGIN.replace(/\/$/, ""),
+    },
   ];
 
   return result;