maarcadetweet: initial commit

AT Protocol PDS + AppView + Tauri Desktop Client, 160-char post limit.

- PDS (Rust + axum + sqlx)
  - Auth: createAccount, createSession, refreshSession
  - Records: createRecord, deleteRecord (race-safe via SELECT FOR UPDATE)
  - Feed: feed.like.create, feed.repost.create
  - Sync: getRepo, getBlocks, getLatestCommit, getRecord (with MST proof), listRepos
  - Identity: resolveHandle
  - MST: spec-conformant (at-mst crate, 27 tests)
  - Repo: signed commits, TID counter (monotonic, 4096 wrap safe)

- AppView (Rust + axum + sqlx)
  - Jetstream consumer (WebSocket, exponential backoff, 38k+ events indexed)
  - REST API: timeline/home (graph-aware), profile, search, post (with thread hydration)
  - Handle-sync worker (did:plc + did:web)
  - JSONB embed storage + thread columns (migration 0003)
  - Like/repost counter cache (migration 0004)

- Tauri 2 + Svelte 5 Desktop Client
  - System tray (Show/Compose/Quit menu)
  - OS notifications (tauri-plugin-notification)
  - Auto-update (tauri-plugin-updater, placeholder endpoint)
  - Window-state (tauri-plugin-window-state)
  - 160-char compose with live counter
  - Image/Link embed rendering
  - LocalStorage-persisted like state
  - Timeline with poll (prepend new posts)
  - Custom TitleBar (transparent, no decorations)
  - Orange/IBM Plex Mono maarcade design

Tests: 231 Rust + 9 vitest = 240 passed.

.gitignore

@@ -0,0 +1,30 @@
+# Rust
+/target
+**/*.rs.bk
+Cargo.lock.bak
+
+# Editors
+.vscode/
+.idea/
+*.swp
+.DS_Store
+
+# Env
+.env
+.env.local
+
+# Node / Tauri frontend
+crates/tauri-app/node_modules/
+crates/tauri-app/dist/
+crates/tauri-app/.svelte-kit/
+crates/tauri-app/.vite/
+crates/tauri-app/src-tauri/target/
+crates/tauri-app/src-tauri/gen/
+crates/tauri-app/src/assets/fonts/*.ttf
+!crates/tauri-app/src/assets/fonts/.gitkeep
+
+# SQLx
+.sqlx/
+
+# Build artifacts
+*.log