Everything on, phase 2 completed: SecureMode on in production, checked by the deploy

Owner decision 2026-10-04: SecureMode on once the pasture passes with it.

- Both clean pasture passes were run over all six peers:
  - normally: 246 passed, 0 failed;
  - with Federation__SecureMode=true: every federation check passed. The only failures were four checks expecting an
    unsigned GET to get 404 or 410 where SecureMode answers 401. Those checks now go through `unserved` and
    `gone_unsigned` (lib/interop.sh), which expect 401 when SecureMode is on.
- Circle posts now reach their member on GoToSocial and Mastodon, and survive Mastodon's signed refetch, as does a
  followers-only post. The GoToSocial expected failure is gone.
- appsettings.Production.json turns SecureMode on.
- The deploy now checks that an unsigned GET of @thepra answers 401 and that a browser is redirected. It reads
  @thepra's discoverability through the Mastodon API, since the actor is no longer readable unsigned.
- docs/INTEROP.md (Mastodon, GoToSocial), CLAUDE.md and ROADMAP updated.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01ELjqpznMFMNrJoJUj6K5p2

tools/pasture/lib/interop.sh

@@ -15,6 +15,13 @@ site() { curl -k --resolve "$1:6443:127.0.0.1" "${@:2}"; }
 pfetch() { curl -sk --connect-to privapub.test:443:127.0.0.1:6443 "$@"; }
 
 # make_png <path>: an 8x8 red PNG, for uploads
+# the status an unsigned ActivityPub GET of a PrivaPub document gets
+pstatus() { pfetch -o /dev/null -w '%{http_code}' -H 'Accept: application/activity+json' "$1"; }
+# SecureMode (PRIVAPUB_ENV="Federation__SecureMode=true") answers every unsigned GET but the instance actor's 401, so a
+# post's author answering 401 means it is on; then 401 is what "not served" and "gone" look like to an unsigned reader
+secure_mode() { [ "$(pstatus "${1%%/scribbles/*}")" = "401" ]; }
+unserved() { local code; code=$(pstatus "$1"); if secure_mode "$1"; then [ "$code" = 401 ]; else [ "$code" = 404 ]; fi; }
+gone_unsigned() { local code; code=$(pstatus "$1"); if secure_mode "$1"; then [ "$code" = 401 ]; else [ "$code" = 410 ]; fi; }
 make_png() { python3 -c "
 import struct,zlib
 w=h=8