Restructure into Cargo workspace with Tauri desktop GUI (#1)

Split the bridge into a tutabridge-core crate, a Tauri v2 desktop app
(src-tauri) and a React/TS UI (ui), keeping the CLI entrypoint at the
workspace root.

Add encrypted local storage (SQLCipher metadata index + encrypted .eml
files) so mail persists across launches and only the delta is fetched.

Wire the bridge to the Tuta Rust SDK via the tuta-repo submodule
(batch loading, MailDetailsBlob reading, interactive 2FA login).

Implement SMTP sending: build the draft and send it through Tuta's
DraftService/SendDraftService, mirroring the web client (body in
compressedBodyText, non-empty sender/recipient names, populated
SendDraftParameters). Add unit tests for the draft/send payload building.

CLAUDE.md

@@ -0,0 +1,61 @@
+# TutaBridge
+
+## Architecture
+
+TutaBridge is an IMAP/SMTP bridge for Tuta encrypted email. It exposes a local IMAP+SMTP server that mail clients (Thunderbird, etc.) connect to.
+
+### Core principle: syncer-driven, store-backed
+
+```
+Tuta API  ←──  Syncer (background)  ──→  MailStore (in-memory)  ←──  IMAP server  ──→  Thunderbird
+                                                                 ←──  Tauri UI (stats)
+```
+
+- The **syncer** (`sync.rs`) runs independently in a background tokio task. It pulls emails from the Tuta API and populates the `MailStore`.
+- The **IMAP server** (`imap/`) ONLY reads from the `MailStore`. It NEVER makes API calls for reads.
+- The only IMAP→network calls are **mutations**: marking read/unread (`STORE \Seen`) and trashing (`EXPUNGE`).
+
+### Syncer two-phase cycle
+
+1. **Phase 1 (fast, ~3s)**: Sync mail lists for ALL 6 folders. Store gets populated with mail metadata immediately.
+2. **Phase 2 (slow, ~2min)**: Prefetch mail details (body) one by one with rate limiting (150ms/mail). Bodies become available progressively.
+3. Wait 60s, repeat.
+
+## Testing
+
+### Unit tests
+
+```bash
+cargo test --workspace        # 113 bridge tests + SDK tests
+```
+
+### Integration test (IMAP)
+
+Requires a running bridge instance (either `cargo run` or `./dev.sh` for GUI).
+
+```bash
+python3 scripts/test_imap.py
+```
+
+This connects to the local IMAP server and verifies: TLS, auth, folder list, mail count, body fetch, search. It reads the bridge password from `~/Library/Application Support/tutabridge/config.toml` automatically.
+
+### Manual Thunderbird test
+
+1. Start bridge: `./dev.sh` (GUI) or `cargo run` (CLI)
+2. Wait for "Pre-fetching N mail details for Inbox" in logs
+3. In Thunderbird: IMAP server `127.0.0.1:1143` SSL/TLS, SMTP `127.0.0.1:1025` SSL/TLS
+4. Username: your tuta email, Password: bridge_password from config
+5. Accept self-signed cert
+
+## Build
+
+```bash
+cargo build                   # CLI + GUI
+cargo build -p tutabridge-core  # Core library only
+```
+
+## SDK branches (tuta-repo submodule)
+
+- `feat/rust-sdk-blob-read` — blob element reading (MailDetailsBlob)
+- `feat/rust-sdk-load-multiple` — batch entity loading (load_multiple)
+- Locally, `feat/rust-sdk-blob-read` has both merged for development