android: the binding generator gets its own crate, free of the app's deps

Third Android run got further than either before it — all four ABIs
cross-compiled, vendored OpenSSL and all — then the generator died:

  error: failed to run custom build command for `openssl-sys v0.9.117`

That is the HOST build. The generator was a [[bin]] inside thoughtsync-ffi, so
building it compiled that crate and therefore the core, reqwest, native-tls and
openssl-sys for linux. The vendored-OpenSSL block is scoped to
`cfg(target_os = "android")`, so the host build went looking for a system
OpenSSL that ci-rust-android has no reason to carry.

Adding libssl-dev to the image would have fixed it and been wrong: a code
generator has no business linking the app's TLS stack to emit Kotlin. Splitting
it into thoughtsync-uniffi-bindgen, whose only dependency is uniffi, removes the
entire chain. Verified from the dependency graph rather than from a build that
happened to succeed — `cargo tree -p thoughtsync-uniffi-bindgen` contains none of
openssl-sys, native-tls, reqwest, thoughtsync-core or rusqlite.

It stays a WORKSPACE MEMBER on purpose. Sharing one lockfile is what keeps uniffi
here and uniffi linked into the .so at one version; they are two halves of one
ABI, and a separate lockfile is precisely how they would drift apart. The cost is
that the desktop lane now compiles ~15 generator crates it never runs — cheap
next to Tauri, and better than leaving the crate unlinted.

Drops the `bindgen` feature and required-features bin from thoughtsync-ffi, which
existed only to keep those crates off the desktop lane and now have nothing to
gate.

Local fmt + clippy + test all green before pushing (107 tests).

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>

android/bindgen/Cargo.toml

@@ -0,0 +1,25 @@
+[package]
+name = "thoughtsync-uniffi-bindgen"
+version = "0.1.0"
+description = "Generates the Kotlin bindings for thoughtsync-ffi"
+authors = ["bvandeusen"]
+edition = "2021"
+
+# A crate whose ONLY dependency is uniffi itself.
+#
+# This started life as a `[[bin]]` inside thoughtsync-ffi, which failed: building
+# it compiled that crate and therefore the core, reqwest, native-tls and
+# openssl-sys — for the HOST. The vendored-OpenSSL block in core/Cargo.toml is
+# scoped to `cfg(target_os = "android")`, so a host build looks for a system
+# OpenSSL that ci-rust-android has no reason to carry, and the generator died
+# with "failed to run custom build command for openssl-sys".
+#
+# Adding libssl-dev to the image would have worked and been wrong: a code
+# generator should not link the app's TLS stack to emit Kotlin. Splitting it out
+# means the generator compiles ~15 small crates and nothing else.
+#
+# Still a WORKSPACE MEMBER, deliberately. That is what keeps `uniffi` here and
+# `uniffi` linked into the .so on one version from one lockfile — they are two
+# halves of one ABI, and a separate lockfile is exactly how they would drift.
+[dependencies]
+uniffi = { version = "0.32", features = ["cli"] }

android/bindgen/src/main.rs

@@ -0,0 +1,16 @@
+//! The Kotlin generator.
+//!
+//! Invoked by Gradle (see android/app/build.gradle.kts) as:
+//!
+//! ```text
+//! cargo run --locked -p thoughtsync-uniffi-bindgen -- \
+//!     generate --library <path/to/libthoughtsync_ffi.so> \
+//!     --language kotlin --out-dir <build/generated/uniffi>
+//! ```
+//!
+//! `--library` mode reads uniffi's metadata straight out of the compiled artifact,
+//! so the generated bindings can never describe a different version of the Rust
+//! than the one being packaged.
+fn main() {
+    uniffi::uniffi_bindgen_main()
+}