feat: add app status tracking to the backend (#17163)

This does ~95% of the backend work required to integrate the AI work.

Most left to integrate from the tasks branch is just frontend, which
will be a lot smaller I believe.

The real difference between this branch and that one is the abstraction
-- this now attaches statuses to apps, and returns the latest status
reported as part of a workspace.

This change enables us to have a similar UX to in the tasks branch, but
for agents other than Claude Code as well. Any app can report status
now.

coderd/database/migrations/000313_workspace_app_statuses.up.sql

@@ -0,0 +1,28 @@
+CREATE TYPE workspace_app_status_state AS ENUM ('working', 'complete', 'failure');
+
+-- Workspace app statuses allow agents to report statuses per-app in the UI.
+CREATE TABLE workspace_app_statuses (
+    id UUID PRIMARY KEY DEFAULT gen_random_uuid(),
+    created_at TIMESTAMP WITH TIME ZONE NOT NULL DEFAULT CURRENT_TIMESTAMP,
+    -- The agent that the status is for.
+    agent_id UUID NOT NULL REFERENCES workspace_agents(id),
+    -- The slug of the app that the status is for. This will be used
+    -- to reference the app in the UI - with an icon.
+    app_id UUID NOT NULL REFERENCES workspace_apps(id),
+	-- workspace_id is the workspace that the status is for.
+	workspace_id UUID NOT NULL REFERENCES workspaces(id),
+    -- The status determines how the status is displayed in the UI.
+    state workspace_app_status_state NOT NULL,
+    -- Whether the status needs user attention.
+    needs_user_attention BOOLEAN NOT NULL,
+    -- The message is the main text that will be displayed in the UI.
+    message TEXT NOT NULL,
+    -- The URI of the resource that the status is for.
+    -- e.g. https://github.com/org/repo/pull/123
+    -- e.g. file:///path/to/file
+    uri TEXT,
+    -- Icon is an external URL to an icon that will be rendered in the UI.
+    icon TEXT
+);
+
+CREATE INDEX idx_workspace_app_statuses_workspace_id_created_at ON workspace_app_statuses(workspace_id, created_at DESC);