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

README.md

@@ -94,17 +94,19 @@ A few things are worth knowing about the first few minutes:
   than broken. It is idempotent — a restart resumes rather than refetches.
 - **The gallery starts empty**, and that is the expected state. Add a creator
   under **Subscriptions** and it fills as posts come down.
-- **If you already have a library on disk**, note that importing it is
-  currently an API call rather than a button — the manual-scan UI was retired
-  in July 2026, when imports started arriving entirely via downloads and the
-  extension. Mount the folder at `./import` and kick it off with:
+- **If you already have a library on disk**, there is no screen that imports
+  it, and there is not going to be one. Folder ingestion had a UI until July
+  2026; it was retired once posts began arriving entirely through
+  subscriptions and the browser extension, and the decision to leave it
+  retired is deliberate — the folder path carries complexity the product does
+  not need in order to do its job. The supported way to fill a new install is
+  to add the creators you follow under **Subscriptions** and let it pull.
 
-  ```bash
-  curl -X POST http://localhost:8080/api/import/trigger
-  ```
-
-  Progress shows up under **Settings → Activity**. This is a known rough
-  edge, not the intended shape (#3367).
+  The `/api/import/trigger` endpoint is still wired up for anyone who wants to
+  script a one-off against a folder mounted at `./import`, and its progress
+  shows under **Settings → Activity**. Treat it as an unsupported escape
+  hatch rather than a feature: nothing in the UI drives it and nothing else
+  in this README depends on it.
 - **To download from a paywalled account**, FabledCurator needs that account's
   session — see the browser extension below. Without one it can still fetch
   public posts.