Fix SNR calculator, add score weight controls, highlight selected filter

SNR calculator: signalFromSB calibration was 4750× too small (0.001 vs ~4.75
at SB=21). Calibration is now derived consistently from the sky background
constants: C[filter] = sky_e_s[filter] / 10^((21 - 21.5) / 2.5). Also made
it filter-aware so narrowband filters use their own reference. Replaced the
broken 500+/billions display with a proper per-filter result or a
'too faint for this setup' message when signal ≈ 0.

Score weights: 'Best score tonight' sort now accepts score_alt/fov/time/moon
query params (0.0–1.0, server-side normalised to sum=1). Frontend adds a
⚙ weights button next to the sort dropdown that reveals 4 sliders showing
effective %, persisted to localStorage. Weights default to 40/30/20/10.

Selected filter: clicking a filter pill in the Filters tab now highlights the
row (bg + amber outline on the pill + ▶ marker) so it's clear which filter
the SNR calculator and workflow card are showing.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

backend/src/api/targets.rs

@@ -65,6 +65,11 @@ pub struct TargetsQuery {
     pub mosaic_only: Option<bool>,
     pub not_imaged: Option<bool>,
     pub show_custom: Option<bool>,
+    // Score weights for "best tonight" sort (0.0–1.0 each, auto-normalised server-side)
+    pub score_alt: Option<f64>,
+    pub score_fov: Option<f64>,
+    pub score_time: Option<f64>,
+    pub score_moon: Option<f64>,
 }
 
 #[derive(Debug, Serialize, sqlx::FromRow)]
@@ -233,18 +238,32 @@ pub async fn list_targets(
     .unwrap_or(1.0);
 
     // "best" sort: composite score balancing altitude, FOV fill, usable time, moon separation.
+    // Weights are normalised to sum=1.0 so changing one factor doesn't need all others to change.
+    let raw_alt  = params.score_alt.unwrap_or(0.40).clamp(0.0, 1.0);
+    let raw_fov  = params.score_fov.unwrap_or(0.30).clamp(0.0, 1.0);
+    let raw_time = params.score_time.unwrap_or(0.20).clamp(0.0, 1.0);
+    let raw_moon = params.score_moon.unwrap_or(0.10).clamp(0.0, 1.0);
+    let weight_sum = raw_alt + raw_fov + raw_time + raw_moon;
+    let (w_alt, w_fov, w_time, w_moon) = if weight_sum > 0.0 {
+        (raw_alt / weight_sum, raw_fov / weight_sum, raw_time / weight_sum, raw_moon / weight_sum)
+    } else {
+        (0.4, 0.3, 0.2, 0.1)
+    };
     // Multiplied by weather_weight so cloudy nights rank all targets lower.
     let best_score_expr = format!(r#"(
-        COALESCE(nc.max_alt_deg, 0) / 90.0 * 0.40
+        COALESCE(nc.max_alt_deg, 0) / 90.0 * {w_alt:.4}
         + CASE
-            WHEN c.fov_fill_pct IS NULL THEN 0.15
-            WHEN c.fov_fill_pct BETWEEN 20 AND 80 THEN (1.0 - ABS(c.fov_fill_pct - 50) / 50.0) * 0.30
-            WHEN c.fov_fill_pct > 80 THEN 0.10
-            ELSE 0.05
+            WHEN c.fov_fill_pct IS NULL THEN {w_fov:.4} * 0.5
+            WHEN c.fov_fill_pct BETWEEN 20 AND 80 THEN (1.0 - ABS(c.fov_fill_pct - 50) / 50.0) * {w_fov:.4}
+            WHEN c.fov_fill_pct > 80 THEN {w_fov:.4} * 0.33
+            ELSE {w_fov:.4} * 0.17
           END
-        + MIN(COALESCE(nc.usable_min, 0), 300) / 300.0 * 0.20
-        + COALESCE(nc.moon_sep_deg, 90) / 180.0 * 0.10
-    ) * {weather_weight:.2} DESC"#, weather_weight = weather_weight);
+        + MIN(COALESCE(nc.usable_min, 0), 300) / 300.0 * {w_time:.4}
+        + COALESCE(nc.moon_sep_deg, 90) / 180.0 * {w_moon:.4}
+    ) * {weather_weight:.2} DESC"#,
+        w_alt = w_alt, w_fov = w_fov, w_time = w_time, w_moon = w_moon,
+        weather_weight = weather_weight
+    );
     let sort_col_owned: String = match params.sort.as_deref() {
         Some("transit") => "nc.transit_utc".to_string(),
         Some("size") => "c.size_arcmin_maj DESC".to_string(),