docs+ci: folder import stays retired, and fix a readiness probe that never probed

Two unrelated things, both found while closing out milestone 328.

**Folder import (#3367).** The operator's call, this session: the
import-from-file surface was abandoned on purpose and is not coming back —
"it has its own complexities that we didn't need." The README and the
compose comment both described the missing button as a rough edge with a
tracking issue, which promised a fix that is not coming. Both now say the
retirement is the decision, name Subscriptions as the supported way to fill
a new install, and describe /api/import/trigger as an unsupported escape
hatch for anyone who wants to script one.

**The CI readiness probe.** ci.yml's integration job and baseline.yml both
waited for Postgres with `(echo > /dev/tcp/$PG_IP/5432)`. Those steps run
under `sh -e` — act's default shell — where /dev/tcp is not a magic path but
a filename that does not exist. The probe could therefore never succeed: run
18035, a GREEN run, spends 05:20:53 → 05:22:53 in that loop and exits it by
exhaustion, not by connecting. Every integration run has been paying a flat
120s for a check that established nothing, and proceeding regardless.

Replaced with a socket connect in python (present in the image, no package
needed), and exhausting the budget is now a named failure instead of a
silent fall-through — rule 156.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01TTjbZZ6JirCMSaJzQV1RhA

docker-compose.yml

@@ -136,9 +136,9 @@ services:
     volumes:
       - ./images:/images
       - ./import:/import
-      # /import is the staging area for ingesting a library you already have
-      # on disk. Drop files in ./import, or bind-mount an existing directory
-      # under it as below, then trigger the scan:
+      # /import is a staging area for scripting a one-off ingest of a library
+      # you already have on disk. Drop files in ./import, or bind-mount an
+      # existing directory under it as below, then trigger the scan:
       #
       #     curl -X POST http://localhost:8080/api/import/trigger
       #
@@ -146,9 +146,11 @@ services:
       # worker + scheduler services mount the same /import so the scan can run
       # on whichever lane picks it up.
       #
-      # There is no UI button for this: the manual-scan surface was retired
-      # 2026-07-02 once imports arrived via downloads + the extension, which is
-      # true for an established install and not for a new one. Tracked in #3367.
+      # Deliberately has no UI. The manual-scan surface was retired 2026-07-02
+      # once imports arrived via subscriptions + the extension, and the call
+      # not to restore it stands (operator, 2026-09-02): folder ingestion
+      # brings complexity the product does not need. The endpoint stays as an
+      # unsupported escape hatch; the supported way in is Subscriptions.
       # - /srv/media/my-library:/import/my-library:ro
     depends_on:
       postgres: { condition: service_healthy }