Make the hackbot UI's address a setting

The apply-side Slack handler had it as a module constant, which was fine while
it was the only thing linking to a run page. It is about to stop being: the
Slack receiver links to one too, when it tells a clicker where the run their
click collapsed onto already is.

A second copy of a hardcoded host is the kind of thing that stays consistent
right up until it does not, so this makes it `settings.hackbot_ui_url` before
there is a second copy rather than after.

Unlike `hackbot_api_url` next to it, this address is never called, only linked,
so the deployed UI is the right default even when running locally: a local link
would be dead for whoever reads the message it lands in.

Author: suhaibmujahid

services/hackbot-api/app/action_handlers/slack_handler.py

@@ -14,11 +14,10 @@
 from slack_sdk import WebClient
 
 from app.action_handlers.base import ActionResult, ApplyContext
+from app.config import settings
 
 log = logging.getLogger(__name__)
 
-_HACKBOT_UI_URL = "https://hackbot.moz.tools"
-
 _TIMEOUT_SECONDS = 30
 
 
@@ -41,7 +40,7 @@ async def apply(self, params: dict[str, Any], ctx: ApplyContext) -> ActionResult
                 "notification_type": "info",
                 "source": {
                     "ref_id": ctx.run_id,
-                    "ref_url": f"{_HACKBOT_UI_URL}/runs/{ctx.run_id}",
+                    "ref_url": f"{settings.hackbot_ui_url}/runs/{ctx.run_id}",
                 },
                 "context": {
                     "agent": ctx.agent,

services/hackbot-api/app/config.py

@@ -94,6 +94,7 @@ class Settings(BaseSettings):
     # is just a matter of repointing this at the remote API. While co-located,
     # this is a loopback call to the same service, authed with external_api_key.
     hackbot_api_url: str = "http://localhost:8080"
+    hackbot_ui_url: str = "https://hackbot.moz.tools"
 
     # Internal event routes (Eventarc / Pub/Sub push targets).
     # Event topics follow a per-domain convention, `<domain>-events` (the GCP