ipx-directory: the directory of public podcasts ipx servers share (#204)

A new crate and service, crates/directory, live at ipx-dir.sdf1.net. ipx
servers send the public feeds their people subscribe to (POST /v1/snapshot,
replacing what that token sent before); the directory fetches each feed's
title, artwork, category, description and latest twenty items every six
hours with ipx-feed, and lists them A to Z and by subscribers summed over
every server. It holds metadata only, never a file or a file's address.

Tokens are in its config file as SHA-256 hashes, each ro, rw or rwa, and
the file is read again within a minute of a change, so adding and revoking
one is an edit and nothing else; a revoked token takes its server's counts.
At first they were to come from environment variables, which would have
meant recreating the container to add one. A file that does not load keeps
the tokens as they were.

Every address sent is checked with ipx_feed::url_looks_private, the check
ipx makes before sending, so one server's miss does not publish a paid feed
to every other; an rwa token can remove and block what both miss.

Deployed: ipx-directory in the ipx Arcane project, database ipx_directory
(its own login) on the databases project's Postgres, which db-backup
already covers, and a tunnel route with no Access in front. The store's
tests run on Postgres as well as SQLite when IPX_TEST_DATABASE_URL is set.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

crates/directory/Cargo.toml

@@ -0,0 +1,27 @@
+[package]
+name = "ipx-directory"
+version.workspace = true
+edition.workspace = true
+
+[[bin]]
+name = "ipx-directory"
+path = "src/main.rs"
+
+[dependencies]
+anyhow.workspace = true
+axum.workspace = true
+clap.workspace = true
+ipx-feed.workspace = true
+reqwest.workspace = true
+sea-orm.workspace = true
+serde.workspace = true
+serde_json.workspace = true
+sha2.workspace = true
+tokio.workspace = true
+toml.workspace = true
+tracing.workspace = true
+tracing-subscriber.workspace = true
+url.workspace = true
+
+[dev-dependencies]
+tower.workspace = true