feat(routing): per-task rules on top of complexity tiers; hosted router is the default

The router has always returned two signals — task label and complexity tier —
but only the tier picked models. [routing.tasks] adds `label → ordered models`:
a matching rule's models lead the candidate chain and the tier chain follows as
fallback, so pinning translations to a local model never weakens failover.
Requests whose chain was headed by a task rule report
route_source "router+task-rule".

The Routing page grows a per-task editor built from the account's LIVE
taxonomy (GET /v1/taxonomies via the new /admin/api/routing/labels proxy;
built-in label set when the router is unreachable), with localized task names,
each task's share of 7-day traffic, "by complexity (no rule)" as the explicit
empty state, and custom labels for other taxonomies. Deleting a model scrubs
it from task rules like it always did from tiers.

Also fixes the default config pointing at a placeholder localhost:8080 router
with a nonexistent taxonomy — a fresh install now targets the hosted allaigate
router (IP endpoint, verify_tls off, data-assistant, 12 s oracle timeout) and
degrades gracefully until a key is set. Verified end-to-end against the live
router: translation → task-rule model, math → tier path.

16 new strings in all 7 languages.

src/pipeline.rs

@@ -232,8 +232,16 @@ impl Pipeline {
                         match live.router.route(&text, prof).await {
                             Ok(Some(dec)) => {
                                 let src = dec.source.clone();
-                                let tier = dec.complexity_tier.clone();
-                                (dec, src, live.routing.candidates(&tier))
+                                let (cands, task_rule) = live
+                                    .routing
+                                    .candidates_for(&dec.task_label, &dec.complexity_tier);
+                                // surface which rule chose the head of the chain
+                                let src = if task_rule {
+                                    format!("{src}+task-rule")
+                                } else {
+                                    src
+                                };
+                                (dec, src, cands)
                             }
                             Ok(None) | Err(_) => {
                                 tracing::warn!(