P1 polish: agent-as-root, init-repo flow, rest creds passthrough, UX fixes

Cohesive batch from a smoke-test session against a real rest-server.
Themed bullets:

* Agent runs as root, sandboxed via systemd. CapabilityBoundingSet
  drops to CAP_DAC_READ_SEARCH + restore caps; ProtectSystem=strict
  with ReadWritePaths confined to /etc + /var/lib/restic-manager;
  NoNewPrivileges blocks escalation. Install script no longer
  creates a service user. spec.md §4.2 / §14.1 / §14.3 explain the
  rationale (matches UrBackup / Veeam / Bareos defaults; trying to
  back up "everything" as an unprivileged user creates silent skips
  on /home, /root, /var/lib/* with no upside vs the threat model
  the agent already implies).

* Init-repo end-to-end. New JobKind="init" wired through agent
  runner, restic.Env.RunInit, server dispatcher, and a UI button
  (red "Initialise repo" in the run-now panel). hosts.repo_initialised_at
  flips on init success, on backup success, or on a non-empty
  snapshots.report. The "Run now" / "Init" / "Retry" branching now
  drives both the dashboard host row and the host-detail panel.
  Migrations 0004 (column), 0005 (jobs.kind CHECK widened — using
  the safe create-new-then-rename pattern; first version corrupted
  job_logs.job_id FK), 0006 (cleans up job_logs FK on already-
  affected DBs).

* rest-server creds embedded at exec time only. restic.Env gains
  RepoUsername; mergeRestCreds() builds the user:pass@-prefixed URL
  inside envSlice() and never assigns it back to the struct, so
  nothing slog-able ever sees the cleartext form. RedactURL helper
  for any future surface that needs to log a URL safely. Both
  helpers tested.

* Add-host UX. Repo password is now optional — server mints a
  24-byte URL-safe random one and surfaces it once, alongside an
  htpasswd snippet ("echo PASS | htpasswd -B -i ... USERNAME") so
  the operator pastes one command on the rest-server host and one
  on the endpoint. Result page also links the install snippet at
  /install/install.sh (was /install.sh — 404'd before) and pipes
  to bash (not sh — script uses set -o pipefail and other
  bashisms; on Debian/Ubuntu sh is dash).

* Late-subscriber race in JobHub. A fast-failing job could finish
  (DB write + Broadcast) before the browser's HX-Redirect → page
  load → WS-connect path completed, so the JS sat forever waiting
  on a job.finished that already passed. JobHub split into
  Register + Send + Run; handleJobStream now subscribes first,
  re-fetches the job, and sends a synthetic job.finished if the
  state is already terminal.

* HTMX error visibility. New toast partial listens to
  htmx:responseError and surfaces the response body as a
  bottom-right toast — every server-side validation error now
  becomes visible without per-handler JS wiring. Also handles
  custom rm:toast events for future server-pushed notifications
  via the HX-Trigger header. Themed via existing CSS vars.

* Dashboard rows are now whole-row clickable to host detail
  (CSS card-link pattern: absolute-positioned anchor + .row-action
  z-index restoration so the action button stays clickable).
  "View →" on a running job links to /jobs/<id> rather than
  /hosts/<id> since the row click already covers the host page.

* "Run first" / "Run first backup" → "Run now" everywhere for
  consistency.

* runbook (docs/e2e-smoke.md) updated — live-log streaming step
  now reflects P1-26; mentions the browser-driven Run-now flow.

* _diag/dump-creds — moved out of cmd/ so go build doesn't pick
  it up; .gitignore now excludes /_diag/ entirely.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

internal/store/hosts.go

@@ -50,7 +50,7 @@ func (s *Store) LookupHostByAgentToken(ctx context.Context, tokenHash string) (*
 			enrolled_at, last_seen_at, status, repo_id, tags,
 			current_job_id, last_backup_at, last_backup_status,
 			repo_size_bytes, snapshot_count, open_alert_count,
-			applied_schedule_version, default_paths
+			applied_schedule_version, default_paths, repo_initialised_at
 		 FROM hosts WHERE agent_token_hash = ?`,
 		tokenHash)
 	return scanHost(row)
@@ -63,7 +63,7 @@ func (s *Store) GetHost(ctx context.Context, id string) (*Host, error) {
 			enrolled_at, last_seen_at, status, repo_id, tags,
 			current_job_id, last_backup_at, last_backup_status,
 			repo_size_bytes, snapshot_count, open_alert_count,
-			applied_schedule_version, default_paths
+			applied_schedule_version, default_paths, repo_initialised_at
 		 FROM hosts WHERE id = ?`, id)
 	return scanHost(row)
 }
@@ -124,7 +124,7 @@ func (s *Store) ListHosts(ctx context.Context) ([]Host, error) {
 			enrolled_at, last_seen_at, status, repo_id, tags,
 			current_job_id, last_backup_at, last_backup_status,
 			repo_size_bytes, snapshot_count, open_alert_count,
-			applied_schedule_version, default_paths
+			applied_schedule_version, default_paths, repo_initialised_at
 		 FROM hosts ORDER BY name`)
 	if err != nil {
 		return nil, fmt.Errorf("store: list hosts: %w", err)
@@ -163,13 +163,14 @@ func scanHostRow(s hostScanner) (*Host, error) {
 		enrolled                      string
 		tags                          string
 		defaultPaths                  string
+		repoInitAt                    sql.NullString
 	)
 	err := s.Scan(&h.ID, &h.Name, &h.OS, &h.Arch,
 		&h.AgentVersion, &h.ResticVersion, &h.ProtocolVersion,
 		&enrolled, &lastSeen, &h.Status, &repoID, &tags,
 		&currentJob, &lastBackupAt, &lastBkSt,
 		&h.RepoSizeBytes, &h.SnapshotCount, &h.OpenAlertCount,
-		&h.AppliedScheduleVersion, &defaultPaths)
+		&h.AppliedScheduleVersion, &defaultPaths, &repoInitAt)
 	if err != nil {
 		if errors.Is(err, sql.ErrNoRows) {
 			return nil, ErrNotFound
@@ -213,5 +214,28 @@ func scanHostRow(s hostScanner) (*Host, error) {
 	if defaultPaths != "" {
 		_ = json.Unmarshal([]byte(defaultPaths), &h.DefaultPaths)
 	}
+	if repoInitAt.Valid {
+		t, err := time.Parse(time.RFC3339Nano, repoInitAt.String)
+		if err != nil {
+			return nil, fmt.Errorf("store: parse repo_initialised_at: %w", err)
+		}
+		h.RepoInitialisedAt = &t
+	}
 	return &h, nil
 }
+
+// MarkHostRepoInitialised sets repo_initialised_at to `when` if it is
+// currently NULL. Idempotent: re-firing for an already-initialised
+// host is a no-op (we never want to clobber the original timestamp).
+// Returns true if the row was updated, false if it was already set.
+func (s *Store) MarkHostRepoInitialised(ctx context.Context, hostID string, when time.Time) (bool, error) {
+	res, err := s.db.ExecContext(ctx,
+		`UPDATE hosts SET repo_initialised_at = ?
+		 WHERE id = ? AND repo_initialised_at IS NULL`,
+		when.UTC().Format(time.RFC3339Nano), hostID)
+	if err != nil {
+		return false, fmt.Errorf("store: mark repo initialised: %w", err)
+	}
+	n, _ := res.RowsAffected()
+	return n > 0, nil
+}