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.

crates/tauri-app/src/lib/components/NavRail.svelte

@@ -0,0 +1,91 @@
+<script lang="ts">
+  type View = "home" | "compose" | "profile" | "search";
+
+  let { current = $bindable<View>("home") }: { current: View } = $props();
+
+  const items: Array<{ id: View; label: string; key: string; icon: string }> = [
+    { id: "home", label: "home", key: "g h", icon: "home" },
+    { id: "compose", label: "compose", key: "c", icon: "compose" },
+    { id: "profile", label: "profile", key: "p", icon: "profile" },
+    { id: "search", label: "search", key: "/", icon: "search" },
+  ];
+</script>
+
+<nav class="rail" aria-label="navigation">
+  {#each items as item}
+    <button
+      class="rail__btn"
+      class:active={current === item.id}
+      onclick={() => (current = item.id)}
+      title={`${item.label}  (${item.key})`}
+      aria-current={current === item.id ? "page" : undefined}
+    >
+      <span class="icon">
+        {#if item.icon === "home"}
+          <svg viewBox="0 0 24 24" fill="none" stroke="currentColor" stroke-width="1.6">
+            <path d="M3 11l9-8 9 8v9a2 2 0 0 1-2 2h-3v-7H8v7H5a2 2 0 0 1-2-2z"/>
+          </svg>
+        {:else if item.icon === "compose"}
+          <svg viewBox="0 0 24 24" fill="none" stroke="currentColor" stroke-width="1.6" stroke-linecap="round">
+            <text x="3" y="17" font-family="ui-monospace,monospace" font-size="14" font-weight="700" fill="currentColor" stroke="none">&gt;_</text>
+          </svg>
+        {:else if item.icon === "profile"}
+          <svg viewBox="0 0 24 24" fill="none" stroke="currentColor" stroke-width="1.6">
+            <circle cx="12" cy="8" r="4"/><path d="M4 21c0-4 4-7 8-7s8 3 8 7"/>
+          </svg>
+        {:else}
+          <svg viewBox="0 0 24 24" fill="none" stroke="currentColor" stroke-width="1.6">
+            <circle cx="11" cy="11" r="7"/><path d="m20 20-3-3"/>
+          </svg>
+        {/if}
+      </span>
+      <span class="label">{item.label}</span>
+    </button>
+  {/each}
+</nav>
+
+<style>
+  .rail {
+    width: 88px;
+    background: var(--bg);
+    border-right: 1px solid var(--line);
+    display: flex;
+    flex-direction: column;
+    gap: var(--s-1);
+    padding: var(--s-3) 0;
+    flex-shrink: 0;
+  }
+  .rail__btn {
+    background: transparent;
+    border: 0;
+    color: var(--text-dim);
+    font-family: var(--font-mono);
+    font-size: var(--fs-50);
+    padding: var(--s-3) var(--s-2);
+    cursor: pointer;
+    display: flex;
+    flex-direction: column;
+    align-items: center;
+    gap: 4px;
+    border-bottom: 1px solid transparent;
+    transition: color var(--dur) var(--ease), border-color var(--dur) var(--ease);
+  }
+  .rail__btn:hover, .rail__btn:focus-visible {
+    color: var(--text);
+  }
+  .rail__btn.active {
+    color: var(--orange);
+    border-bottom-color: var(--orange);
+  }
+  .icon {
+    width: 24px;
+    height: 24px;
+    display: grid;
+    place-items: center;
+  }
+  .icon :global(svg) {
+    width: 22px;
+    height: 22px;
+  }
+  .label { letter-spacing: 0.04em; }
+</style>