🐳 build: fix Dockerfile by adding ptth_tail skeleton

It's a bit silly, but because of the workspace setup, we can't build
ptth_relay unless all the other projects have a skeleton.

Dockerfile

@@ -17,9 +17,10 @@ WORKDIR /ptth
 RUN \
 cargo new --lib crates/always_equal && \
 cargo new --lib crates/ptth_core && \
-cargo new --bin crates/ptth_file_server_bin && \
 cargo new --bin crates/ptth_relay && \
-cargo new --bin crates/ptth_server
+cargo new --bin crates/ptth_server && \
+cargo new --bin crates/ptth_file_server_bin && \
+cargo new --bin tools/ptth_tail
 
 # copy over your manifests
 COPY ./Cargo.lock                               ./
@@ -27,8 +28,9 @@ COPY ./Cargo.toml                     ./
 COPY ./crates/always_equal/Cargo.toml           ./crates/always_equal/
 COPY ./crates/ptth_core/Cargo.toml              ./crates/ptth_core/
 COPY ./crates/ptth_relay/Cargo.toml             ./crates/ptth_relay/
-COPY ./crates/ptth_file_server_bin/Cargo.toml   ./crates/ptth_file_server_bin/
-COPY ./crates/ptth_server/Cargo.toml   ./crates/ptth_server/
+# COPY ./crates/ptth_server/Cargo.toml            ./crates/ptth_server/
+# COPY ./crates/ptth_file_server_bin/Cargo.toml   ./crates/ptth_file_server_bin/
+# COPY ./tools/ptth_tail/Cargo.toml               ./tools/ptth_tail/
 
 # this build step will cache your dependencies
 RUN cargo build --release -p ptth_relay
@@ -38,15 +40,15 @@ rm \
 src/*.rs \
 crates/always_equal/src/*.rs \
 crates/ptth_core/src/*.rs \
-crates/ptth_file_server_bin/src/*.rs \
-crates/ptth_relay/src/*.rs \
-crates/ptth_server/src/*.rs
+crates/ptth_relay/src/*.rs
 
 # Copy source tree
 # Yes, I tried a few variations on the syntax. Dockerfiles are just rough.
 
 COPY ./src/                ./src
-COPY ./crates/ ./crates
+COPY ./crates/always_equal ./crates/always_equal
+COPY ./crates/ptth_core    ./crates/ptth_core
+COPY ./crates/ptth_relay   ./crates/ptth_relay
 COPY ./handlebars/         ./handlebars
 
 # Bug in cargo's incremental build logic, triggered by