P3 follow-up: editable target dir, conditional --no-ownership, UK lint

Three small follow-ups from review:

1. Restore target is now operator-editable. Default value is the
   literal '\$HOME/rm-restore/<job-id>/' (agent expands \$HOME at
   run time using os.UserHomeDir(); also handles \${HOME} and ~/
   prefixes). Operator can replace with any absolute path.
   - ui_restore.go validates the input is either absolute or starts
     with one of the recognised prefixes; other env-var refs (\$PATH
     etc.) are deliberately rejected so operator paths can't pick up
     arbitrary agent env values.
   - host_restore.html replaces the read-only mono-text display with
     a real <input>; help text spells out that \$HOME resolves
     agent-side and <job-id> is substituted on dispatch.
   - install.sh + the systemd unit prep /root/rm-restore so the
     default works under the sandbox: ReadWritePaths gains a soft
     '-/root/rm-restore' entry (the '-' makes the bind-mount soft-fail
     if missing, but install.sh pre-creates it root-owned 0700).

2. --no-ownership flag now gated on restic version. The flag was
   added in restic 0.17 and 0.16 rejects it. Previously dropped it
   wholesale — that meant new-dir restores silently preserved
   ownership against design intent on 0.17+. Now the agent threads
   its detected restic version (sysinfo already collects it) through
   runner.Config -> restic.Env, and RunRestore appends --no-ownership
   only when AtLeastVersion(0, 17) returns true. 0.16 hosts still
   restore with original uid/gid; help text in the wizard explicitly
   notes this. The previous 'Original ownership is preserved' copy
   was wrong for new-dir mode and is corrected.

3. golangci-lint misspell locale switched US -> UK and the codebase
   swept (73 corrections, mostly behaviour/serialise/recognise/honour).
   Wire-format ErrorCode 'unauthorized' -> 'unauthorised' is a tiny
   contract change but the agent doesn't parse those codes today and
   no external API consumers exist yet. Tests passed before + after.

Tests:
- internal/restic/version_test.go covers Env.AtLeastVersion across
  edge cases (empty, exact match, patch above, minor below, non-
  numeric) and expandHome on \$HOME / \${HOME} / ~/, plus
  pass-through for absolute paths and refusal of other env vars.
- ui_restore_test updated: TargetDir now starts '\$HOME/rm-restore/'
  with the job_id substituted into the placeholder.

Live verified on the smoke env: default target restored to
/root/rm-restore/<job-id>/ as the agent's expanded \$HOME (2 files,
14 bytes); custom override '/tmp/custom-restore/<job-id>/' restored
into the agent's PrivateTmp namespace (1 file, 6 bytes); both jobs
'succeeded', exit 0.

internal/restic/version_test.go

@@ -0,0 +1,64 @@
+package restic
+
+import (
+	"path/filepath"
+	"testing"
+)
+
+func TestEnvAtLeastVersion(t *testing.T) {
+	t.Parallel()
+	cases := []struct {
+		ver       string
+		major     int
+		minor     int
+		want      bool
+		shortDesc string
+	}{
+		{"0.17.0", 0, 17, true, "exact match"},
+		{"0.17.1", 0, 17, true, "patch above"},
+		{"0.18.0", 0, 17, true, "minor above"},
+		{"1.0.0", 0, 17, true, "major above"},
+		{"0.16.4", 0, 17, false, "minor below"},
+		{"0.16", 0, 17, false, "two-part minor below"},
+		{"", 0, 17, false, "empty"},
+		{"v0.17", 0, 17, false, "prefixed v rejected"},
+		{"unknown", 0, 17, false, "non-numeric rejected"},
+	}
+	for _, c := range cases {
+		got := Env{Version: c.ver}.AtLeastVersion(c.major, c.minor)
+		if got != c.want {
+			t.Errorf("AtLeastVersion(%q, %d, %d): got %v want %v · %s",
+				c.ver, c.major, c.minor, got, c.want, c.shortDesc)
+		}
+	}
+}
+
+func TestExpandHome(t *testing.T) {
+	// Not parallel — t.Setenv on HOME would race with sibling tests.
+	tmp := t.TempDir()
+	t.Setenv("HOME", tmp)
+
+	cases := []struct {
+		in, want string
+	}{
+		{"$HOME/rm-restore/job-1/", filepath.Join(tmp, "rm-restore/job-1")},
+		{"${HOME}/rm-restore/job-2/", filepath.Join(tmp, "rm-restore/job-2")},
+		{"~/rm-restore/job-3/", filepath.Join(tmp, "rm-restore/job-3")},
+		{"$HOME", tmp},
+		{"~", tmp},
+		{"/var/lib/x/y", "/var/lib/x/y"}, // absolute path passes through
+		{"", ""},
+		{"$PATH/foo", "$PATH/foo"}, // other env vars not expanded
+	}
+	for _, c := range cases {
+		got := expandHome(c.in)
+		if got != c.want {
+			t.Errorf("expandHome(%q): got %q want %q", c.in, got, c.want)
+		}
+	}
+
+	// Sanity: an absolute path always passes through regardless of HOME.
+	if got := expandHome("/abs"); got != "/abs" {
+		t.Errorf("expandHome(/abs): got %q", got)
+	}
+}