feat: PR filter — compare models on the same set of PRs

UI: a repo#pr multi-select (labeled with how many models ran each PR)
scopes the whole table — runs, minutes, findings, points — to the chosen
PRs, so a model with 2 runs can be fairly compared against one with 60.
API: GET /scoreboard accepts ?repo= and ?pr= (repeatable or comma-list).

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

server.go

@@ -5,6 +5,7 @@ import (
 	"errors"
 	"log"
 	"net/http"
+	"strconv"
 	"strings"
 )
 
@@ -21,7 +22,9 @@ import (
 //	GET  /healthz     liveness                                         (public)
 //	GET  /runs        list all runs (timing/tokens), oldest first
 //	GET  /export      flat report×finding×grade rows (the dashboard feed)
-//	GET  /scoreboard  points-free per-model rollup
+//	GET  /scoreboard  points-free per-model rollup; ?repo= and ?pr= (repeatable
+//	                  or comma-list) narrow it to specific PRs so models are
+//	                  compared on the same work
 //	POST /runs                     upsert one run (model review of a PR; timing/tokens)
 //	POST /reports                  record a batch of findings + this model's reports
 //	POST /findings/{id}/grade      record a triage grade (is_real, severity, …)
@@ -79,8 +82,24 @@ func newServer(store *Store, token string) http.Handler {
 		writeJSON(w, http.StatusOK, rows)
 	})
 
-	mux.HandleFunc("GET /scoreboard", func(w http.ResponseWriter, _ *http.Request) {
-		stats, err := store.Scoreboard()
+	mux.HandleFunc("GET /scoreboard", func(w http.ResponseWriter, r *http.Request) {
+		f := ScoreboardFilter{Repo: r.URL.Query().Get("repo")}
+		// pr is repeatable and accepts comma lists: ?pr=1&pr=2 or ?pr=1,2
+		for _, v := range r.URL.Query()["pr"] {
+			for part := range strings.SplitSeq(v, ",") {
+				part = strings.TrimSpace(part)
+				if part == "" {
+					continue
+				}
+				n, err := strconv.Atoi(part)
+				if err != nil {
+					writeErr(w, http.StatusBadRequest, errors.New("invalid pr number: "+part))
+					return
+				}
+				f.PRs = append(f.PRs, n)
+			}
+		}
+		stats, err := store.Scoreboard(f)
 		if err != nil {
 			writeErr(w, http.StatusInternalServerError, err)
 			return