feat(desktop): runtime-configurable backend server address

The desktop shell is one generic .deb/.AppImage distributed via
mca/public_releases, not built per-booth, but the backend origin was baked
in at build time (VITE_API_BASE, hardcoded to http://127.0.0.1:3000) — the
same installer could never point at a different appliance without a
rebuild.

Adds ConnectScreen (shown before Login in Tauri when no backend is saved),
backed by tauri-plugin-store persisting the operator-entered URL across
restarts. CSP's connect-src tightens to 'self' only — all backend traffic
already routes through tauri-plugin-http/websocket, which run Rust-side
and are outside connect-src's reach anyway — and the real access boundary
moves to capabilities/default.json's http:default scope, wildcarded so an
operator-chosen host is actually reachable. Adds a "Change server" control
in Setup (desktop-only) to repoint an already-configured install.

While tracing the desktop auth path for this: tauri-plugin-http's fetch()
runs through Rust's reqwest, which keeps its own cookie jar separate from
the webview, so document.cookie on tauri://localhost never sees the
parking_csrf cookie the server sets (open upstream bug,
tauri-apps/tauri#13045/#11518). This means the desktop app has likely been
silently sending no CSRF header on every mutation since the shell was
first built — pre-existing, independent of this change. Fixed by having
sessionView() (routes/auth.ts) also echo the CSRF value in the login/me
JSON body; the desktop client stashes it in memory and echoes that instead
of reading document.cookie. assertCsrf() itself is untouched.

Verified end-to-end against a real LAN-bound dev server: login returns a
csrfToken matching the cookie, a mutation using the body-sourced token in
X-CSRF-Token succeeds (200), and the same mutation without it still
correctly 403s.

apps/server/src/routes/auth.ts

@@ -65,7 +65,21 @@ function cleanProfileField(v: string | null | undefined): string | null | undefi
 
 /** The session shape the SPA bootstraps from: identity + role + its permission
  *  list (so the UI can gate nav/routes) + language. Role NAME is for display; the
- *  permissions are the source of truth. */
+ *  permissions are the source of truth.
+ *
+ *  `csrf`, when passed, echoes the SAME value already sent as the readable
+ *  parking_csrf cookie — not a new secret, just a second channel to learn it.
+ *  The desktop shell needs this: tauri-plugin-http's fetch() runs through
+ *  Rust's reqwest, which keeps its own cookie jar separate from the webview,
+ *  so document.cookie on the tauri://localhost page never sees a cookie set
+ *  on a plugin-routed response (open upstream bug, tauri-apps/tauri#13045).
+ *  The cookie itself IS still sent back to the server by reqwest on
+ *  subsequent requests — only the *client-side read* is broken — so
+ *  api.ts's desktop path stashes this body value in memory instead of
+ *  reading document.cookie, and echoes it in X-CSRF-Token exactly as the
+ *  browser path echoes the cookie. See lib/api.ts and assertCsrf() in
+ *  ../auth.ts (unchanged — this never touches verification, only how the
+ *  desktop client learns what to send). */
 function sessionView(
   db: Db,
   user: {
@@ -78,6 +92,7 @@ function sessionView(
     fullName?: string | null;
     email?: string | null;
   },
+  csrf?: string,
 ) {
   const role = db.select().from(roles).where(eq(roles.id, user.roleId)).get();
   const permissions = [...permissionsFor(user.roleId)];
@@ -92,6 +107,7 @@ function sessionView(
     fontScale: user.fontScale,
     fullName: user.fullName ?? null,
     email: user.email ?? null,
+    ...(csrf ? { csrfToken: csrf } : {}),
   };
 }
 
@@ -126,7 +142,7 @@ export async function authRoutes(app: FastifyInstance, db: Db): Promise<void> {
     setAuthCookies(reply, token, csrf);
     // `language` is NOT in the JWT (identity/role only) — it's a mutable preference
     // read from the DB, so changing it needs no token refresh.
-    return sessionView(db, user);
+    return sessionView(db, user, csrf);
   });
 
   app.post("/api/auth/logout", async (_req, reply) => {
@@ -146,7 +162,9 @@ export async function authRoutes(app: FastifyInstance, db: Db): Promise<void> {
         clearAuthCookies(reply);
         return reply.code(401).send({ error: "session no longer valid" });
       }
-      return sessionView(db, row);
+      // req.user.csrf is the value bound into the JWT at login (see assertCsrf in
+      // ../auth.ts) — same value as the cookie, re-surfaced for the desktop path.
+      return sessionView(db, row, req.user.csrf);
     },
   );