feat(admin): the nightly backup, made visible

It has run since the beginning and nothing showed it. A backup nobody can see is
a backup nobody knows has been failing, and the failure is quiet: a volume gone
read-only, a disk that filled, a container that has not been up at midnight all
week. The first anybody hears of it is the day they need one.

`ListBackupRuns` was already in the store and exposed nowhere. Now there is a
list, a download, and a button that takes one now — the same work the nightly job
does without its "one a day" check, because waiting until tonight to learn whether
backups work at all is how somebody finds out on the day they need one, and it is
the only way to get a snapshot from *before* something you are about to do.

Restoring is deliberately not a button. Swapping a database under a server that
is writing to it means stopping every writer, replacing the file and reopening,
and a half-done version of that destroys the thing it was restoring. The panel
says what to do instead.

`RunBackupNow` turns out to have been a second copy of the backup logic, written
for a button that did not exist yet, and the two had already drifted: it never
created the backups directory and logged nothing. One implementation now.

Administrators only, and sessions only. A backup is a complete copy of the
database, so this hands out everybody's data in one file.

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

internal/httpapi/backup_handlers.go

@@ -0,0 +1,158 @@
+package httpapi
+
+import (
+	"fmt"
+	"net/http"
+	"os"
+	"path/filepath"
+	"strings"
+	"time"
+
+	"github.com/go-chi/chi/v5"
+
+	"github.com/kristianwind/verdande/internal/jobs"
+)
+
+// The nightly backup, made visible.
+//
+// It has run since the beginning and nothing showed it. A backup nobody can see is
+// a backup nobody knows has been failing — and the failure mode is quiet: a volume
+// that went read-only, a disk that filled, a container that has not been up at
+// midnight for a week. The first time anybody finds out is the day they need one.
+//
+// Administrators only, and behind a session as well as the admin check. A backup
+// file is a complete copy of the database, so downloading one is downloading
+// everybody's data; a leaked API token must not be able to.
+
+type backupRunJSON struct {
+	ID      string `json:"id"`
+	Started string `json:"started_at"`
+	// Finished is absent while a backup is still running, and on one that was
+	// interrupted — which is the same shape from outside and honestly so: a run
+	// the process died in the middle of never finished.
+	Finished string `json:"finished_at,omitempty"`
+	Size     int64  `json:"size_bytes"`
+	Error    string `json:"error,omitempty"`
+	// Present says the file is still on disk. Rotation keeps the most recent
+	// fourteen, so an older row is a true record of a backup that was made and a
+	// file that is no longer there — and a download link for it would 404.
+	Present bool `json:"present"`
+}
+
+func (s *Server) handleListBackups(w http.ResponseWriter, r *http.Request) {
+	runs, err := s.db.ListBackupRuns(r.Context(), parseLimit(r.URL.Query().Get("limit"), 30, 100))
+	if err != nil {
+		s.internal(w, r, "list backups", err)
+		return
+	}
+
+	out := make([]backupRunJSON, 0, len(runs))
+	for _, b := range runs {
+		j := backupRunJSON{
+			ID: b.ID, Started: b.StartedAt.Format(time.RFC3339),
+			Size: b.SizeBytes, Error: b.Error,
+		}
+		if b.FinishedAt != nil {
+			j.Finished = b.FinishedAt.Format(time.RFC3339)
+		}
+		if b.Path != "" {
+			if _, err := os.Stat(b.Path); err == nil {
+				j.Present = true
+			}
+		}
+		out = append(out, j)
+	}
+	writeJSON(w, http.StatusOK, map[string]any{"backups": out})
+}
+
+// handleRunBackup takes one now.
+//
+// The same function the nightly job runs, without the "has one run today" check.
+// Waiting until tonight to learn whether backups work at all is how somebody finds
+// out on the day they need one — and it is the only way to get a snapshot from
+// *before* something you are about to do.
+//
+// Synchronous. A backup of a homelab database is a second or two, and a button
+// that returns immediately and tells you nothing is a button you press twice.
+func (s *Server) handleRunBackup(w http.ResponseWriter, r *http.Request) {
+	if err := jobs.Backup(r.Context(), s.cfg, s.db, s.log); err != nil {
+		s.internal(w, r, "run backup", err)
+		return
+	}
+	runs, err := s.db.ListBackupRuns(r.Context(), 1)
+	if err != nil || len(runs) == 0 {
+		w.WriteHeader(http.StatusNoContent)
+		return
+	}
+	b := runs[0]
+	j := backupRunJSON{
+		ID: b.ID, Started: b.StartedAt.Format(time.RFC3339),
+		Size: b.SizeBytes, Error: b.Error, Present: true,
+	}
+	if b.FinishedAt != nil {
+		j.Finished = b.FinishedAt.Format(time.RFC3339)
+	}
+	writeJSON(w, http.StatusCreated, j)
+}
+
+// handleDownloadBackup sends one backup file.
+//
+// The path comes from the row rather than from the request, and is then checked to
+// be inside the backups directory anyway. The row is written by this process and
+// should always be safe; the check is there because "should always" is how a path
+// traversal gets shipped, and the thing on the other side of it is every account's
+// data in one file.
+func (s *Server) handleDownloadBackup(w http.ResponseWriter, r *http.Request) {
+	runs, err := s.db.ListBackupRuns(r.Context(), 100)
+	if err != nil {
+		s.internal(w, r, "list backups", err)
+		return
+	}
+
+	id := chi.URLParam(r, "backupID")
+	var path string
+	for _, b := range runs {
+		if b.ID == id {
+			path = b.Path
+			break
+		}
+	}
+	if path == "" {
+		writeError(w, http.StatusNotFound, CodeNotFound, "not found")
+		return
+	}
+
+	dir, err := filepath.Abs(s.cfg.BackupsDir())
+	if err != nil {
+		s.internal(w, r, "backups dir", err)
+		return
+	}
+	full, err := filepath.Abs(path)
+	if err != nil || !strings.HasPrefix(full, dir+string(os.PathSeparator)) {
+		writeError(w, http.StatusNotFound, CodeNotFound, "not found")
+		return
+	}
+	file, err := os.Open(full)
+	if err != nil {
+		// Rotation keeps the most recent fourteen, so a row older than that is a
+		// true record with no file behind it. Not an error — a 404 is the honest
+		// answer to "send me that one".
+		writeError(w, http.StatusNotFound, CodeNotFound, "not found")
+		return
+	}
+	defer file.Close()
+
+	info, err := file.Stat()
+	if err != nil {
+		s.internal(w, r, "stat backup", err)
+		return
+	}
+
+	// The same treatment attachments get, and for a stronger reason: this is a
+	// SQLite database, and nothing should ever be tempted to render it inline.
+	w.Header().Set("Content-Type", "application/octet-stream")
+	w.Header().Set("Content-Disposition",
+		fmt.Sprintf("attachment; filename=%q", filepath.Base(full)))
+	w.Header().Set("X-Content-Type-Options", "nosniff")
+	http.ServeContent(w, r, "", info.ModTime(), file)
+}