core: extract the store and sync engine into a shared crate (M12 step 1)

Android becomes a native Kotlin client over this same code (Scribe note 2730), so
the local store and sync engine stop being modules of the desktop app and become
`thoughtsync-core`, a crate with no UI framework in it at all.

This is a move, not a rewrite, and the measurement is why: every file in local/
and sync/ already carried ZERO Tauri references — 4,980 of 6,372 lines. The
coupling was 473 lines of command shim, which stays behind in the desktop crate
as src/commands/. Kept as git renames so history follows the files.

The desktop imports them under their old names (`use thoughtsync_core::{local,
sync}`) so every call site reads exactly as before. What moved is where they
live, not what they are.

Two things a workspace changes that are easy to miss, both caught before pushing:

[profile.release] now lives at the workspace ROOT. Cargo silently ignores
profiles declared by a non-root member — leaving it in the desktop crate would
have dropped lto/strip/opt-level from every release build with only a warning.

And a workspace shares ONE target dir, so the bundles moved from
desktop/src-tauri/target to target/. Thirteen references across publish-release,
debundle-graphics, verify.sh, package-prebuilt and the workflow now point there.
Pinning target-dir back would have been the smaller diff, but the Android lane
also produces Rust artifacts and they do not belong under desktop/.

Also retires the Tauri Android lane in the same push rather than leaving a path
that is being replaced: gen/android, android.yml and docs/android-dev.md are
gone, the mobile_entry_point attribute with them, and the lib drops to rlib —
staticlib/cdylib existed for Tauri mobile, and the .so Android loads will be
built from the core crate instead. Rule 22, no parallel path.

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

desktop/src-tauri/src/update.rs

@@ -21,7 +21,7 @@ use serde::{Deserialize, Serialize};
 use tauri::State;
 use tauri_plugin_updater::UpdaterExt;
 
-use crate::local::{store, Db};
+use thoughtsync_core::local::{store, Db};
 
 /// Where the manifests live. Fixed tags, so these URLs are permanent.
 const FEED_BASE: &str = "https://git.fabledsword.com/bvandeusen/thoughtsync/releases/download";
@@ -308,9 +308,9 @@ fn describe_check_error(detail: &str) -> String {
 #[cfg(test)]
 mod tests {
     use super::*;
-    use crate::local::schema;
     use rusqlite::Connection;
     use std::sync::Mutex;
+    use thoughtsync_core::local::schema;
 
     fn db() -> Db {
         let conn = Connection::open_in_memory().expect("in-memory db");