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/restic/runner.go

@@ -33,10 +33,19 @@ func Locate(override string) (string, error) {
 }
 
 // Env is the per-invocation context for a restic command.
+//
+// RepoURL is the bare URL as the operator typed it — no embedded
+// credentials. RepoUsername (optional) carries the HTTP basic-auth
+// user for `rest:` repos. The merged URL (with `user:pass@host`
+// embedded) is built once inside envSlice() at the moment of exec
+// and fed straight to the subprocess via RESTIC_REPOSITORY; we
+// never assign it back to Env, never pass it to slog. If anything
+// in this package ever needs to *log* a URL, use RedactURL.
 type Env struct {
 	Bin           string            // path to restic binary
-	RepoURL       string            // RESTIC_REPOSITORY
-	RepoPassword  string            // RESTIC_PASSWORD (passed via env, never argv)
+	RepoURL       string            // RESTIC_REPOSITORY (no embedded creds)
+	RepoUsername  string            // optional HTTP basic-auth user for rest: URLs
+	RepoPassword  string            // doubles as RESTIC_PASSWORD and (for rest:) HTTP basic-auth password
 	ExtraEnv      map[string]string // any other RESTIC_* / passthrough
 	WorkDir       string            // CWD; default = current
 }
@@ -140,6 +149,55 @@ func (e Env) RunBackup(ctx context.Context, paths, excludes, tags []string, hand
 	return summary, nil
 }
 
+// RunInit executes `restic init` against the configured repo. Returns
+// nil on success. Restic init's output is small and not JSON-rich;
+// we tee stdout/stderr verbatim through handle so the operator sees
+// the same lines they'd see at the CLI ("created restic repository
+// <id> at <url>" on success, "config file already exists" on a
+// re-init attempt, etc.).
+func (e Env) RunInit(ctx context.Context, handle LineHandler) error {
+	cmd := exec.CommandContext(ctx, e.Bin, "init")
+	cmd.Env = e.envSlice()
+	cmd.Dir = e.WorkDir
+
+	stdout, err := cmd.StdoutPipe()
+	if err != nil {
+		return fmt.Errorf("restic init: stdout pipe: %w", err)
+	}
+	stderr, err := cmd.StderrPipe()
+	if err != nil {
+		return fmt.Errorf("restic init: stderr pipe: %w", err)
+	}
+
+	if err := cmd.Start(); err != nil {
+		return fmt.Errorf("restic init: start: %w", err)
+	}
+
+	done := make(chan error, 2)
+	go func() { done <- pumpPlain(stdout, "stdout", handle) }()
+	go func() { done <- pumpPlain(stderr, "stderr", handle) }()
+	for i := 0; i < 2; i++ {
+		if err := <-done; err != nil && handle != nil {
+			handle("event", fmt.Sprintf("pump error: %v", err), nil)
+		}
+	}
+	if werr := cmd.Wait(); werr != nil {
+		return fmt.Errorf("restic init: %w", werr)
+	}
+	return nil
+}
+
+func pumpPlain(r io.Reader, stream string, handle LineHandler) error {
+	scanner := bufio.NewScanner(r)
+	scanner.Buffer(make([]byte, 0, 64*1024), 1024*1024)
+	for scanner.Scan() {
+		if handle != nil {
+			handle(stream, scanner.Text(), nil)
+		}
+	}
+	return scanner.Err()
+}
+
 // envSlice converts Env's typed fields into the os/exec env shape.
 //
 // Deliberately does NOT inherit the parent process's environment:
@@ -164,7 +222,7 @@ func (e Env) envSlice() []string {
 		xdg = x
 	}
 	out := []string{
-		"RESTIC_REPOSITORY=" + e.RepoURL,
+		"RESTIC_REPOSITORY=" + mergeRestCreds(e.RepoURL, e.RepoUsername, e.RepoPassword),
 		"RESTIC_PASSWORD=" + e.RepoPassword,
 		// Feed restic via env-only — keeps creds off ps(1).
 		"PATH=/usr/local/bin:/usr/bin:/bin",