Cargo workspace: crates/ipx and a shared crates/feed (#202)

The first step of the split (#207). The daemon moves to crates/ipx unchanged;
feed.rs becomes crates/feed (ipx-feed), which the directory service (#204)
will share for its metadata refresher and its privacy check.

To stand alone, fetch takes the feed's address and its credentials instead
of ipx's config::Feed (config::Feed::auth gives them), collect_outlines
moves in with the OPML parsing, and the address half of looks_private is
feed::url_looks_private. ipx imports the crate as `feed` at its root, so
every crate::feed path is unchanged. The version is the workspace's, in the
root Cargo.toml.

Checked: cargo test on Postgres (118 + 29), tsc, page smoke, native bridge,
contrast and Playwright (72) pass; the image built from the new Dockerfile
is deployed and healthy.

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

Dockerfile

@@ -11,17 +11,20 @@ WORKDIR /src
 COPY package.json package-lock.json ./
 RUN npm ci --omit=dev
 
-# Dependencies first, so editing the source does not rebuild librqbit every time.
+# Dependencies first, so editing the source does not rebuild librqbit every time: each crate of
+# the workspace as an empty stub, its manifest real.
 COPY Cargo.toml Cargo.lock ./
-RUN mkdir src && echo 'fn main(){}' > src/main.rs \
+COPY crates/ipx/Cargo.toml crates/ipx/
+COPY crates/feed/Cargo.toml crates/feed/
+RUN mkdir -p crates/ipx/src crates/feed/src \
+    && echo 'fn main(){}' > crates/ipx/src/main.rs && touch crates/feed/src/lib.rs \
     && cargo build --release --locked \
-    && rm -rf src
+    && rm -rf crates/ipx/src crates/feed/src
 
-COPY build.rs ./
-COPY src ./src
+COPY crates ./crates
 COPY web ./web
 # cargo skips a rebuild if mtimes look untouched; make sure it does not.
-RUN touch src/main.rs && cargo build --release --locked
+RUN touch crates/ipx/src/main.rs crates/feed/src/lib.rs && cargo build --release --locked
 
 FROM debian:trixie-slim
 # ffmpeg is DeadAir's (#171): it finds the silences and copies the frames kept. Debian's adds