Add repo-detail panel and /api/repo endpoint

New <repo-detail> component listens for repo:select and shows a repo's remotes, local branches (current + upstream), and recent commits. Backed by GET /api/repo (restricted to indexed repos) and read-only git readers LocalBranches/RecentCommits/RemoteDetails via repos.BuildDetail. <repo-list> highlights the selection; page docks the two panels left/right.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

cmd/server/main.go

@@ -8,6 +8,7 @@ import (
 	"net/http"
 	"os"
 	"os/signal"
+	"path/filepath"
 	"syscall"
 	"time"
 
@@ -80,6 +81,17 @@ func main() {
 	e.GET("/api/repos", func(c echo.Context) error {
 		return c.JSON(http.StatusOK, scanner.Index.List())
 	})
+	e.GET("/api/repo", func(c echo.Context) error {
+		// Only serve details for a repo we already discovered — never run git
+		// against an arbitrary path supplied in the query string. Clean the
+		// input so separator style (/, \) doesn't defeat the exact-match lookup.
+		path := filepath.Clean(c.QueryParam("path"))
+		base, ok := scanner.Index.Get(path)
+		if !ok {
+			return c.JSON(http.StatusNotFound, map[string]string{"error": "unknown repository"})
+		}
+		return c.JSON(http.StatusOK, repos.BuildDetail(c.Request().Context(), g, base))
+	})
 
 	// Serve with graceful shutdown.
 	go func() {