feat(routing): linked complexity-boundary sliders — your own low/medium/high

The tier boundaries lived on the router and were global for every customer
of a hosted router; per-gateway tuning meant hand-editing score ranges. The
Routing page now has one track with two draggable handles (the low|medium
and medium|high boundaries) over three colored zones: handles push each
other (low can't cross medium — it shoves it along, and vice versa), the
numbers ride on the handles and the legend updates live, so nobody types
ranges by hand. Unchecked = the router's own bands, untouched behavior.

Under the hood the gateway re-maps the router's CONTINUOUS complexity score
with the user's boundaries ([routing.bands] low/medium in gateway.toml,
validated 0 < low < medium < 1) before tier chains, escalation and stats —
verified live: with bands at 0.70/0.72 a score-0.27 request that used to be
medium routed low, and back after restoring the defaults.

2 new strings in all 7 languages.

src/pipeline.rs

@@ -231,6 +231,19 @@ impl Pipeline {
                         let prof = profile.as_deref().unwrap_or(&live.cfg.route.profile);
                         match live.router.route(&text, prof).await {
                             Ok(Some(dec)) => {
+                                let mut dec = dec;
+                                // per-gateway complexity bands: re-map the
+                                // router's continuous score with the user's
+                                // own boundaries (sliders on the Routing page)
+                                if let Some(b) = &live.cfg.routing.bands {
+                                    if matches!(
+                                        dec.complexity_tier.as_str(),
+                                        "low" | "medium" | "high"
+                                    ) {
+                                        dec.complexity_tier =
+                                            b.tier_of(dec.complexity_score).to_string();
+                                    }
+                                }
                                 let src = dec.source.clone();
                                 let (cands, task_rule) = live
                                     .routing