fix(main): hoist let bindings to top of start() to fix TDZ on anchorError

The applyMode() function reads/writes anchorError, lastSnapshot, and other
let-bound state. Function declarations are hoisted, so applyMode() can fire
from inside the dialog.mount() / applyMode() call sequence at the top of
start() — but the let bindings themselves are not initialized until
execution reaches their declaration line, which came later.

When prefs.mode === 'anchored' and findAnchorElement() returns null, the
new 'anchor missed' branch writes to anchorError and calls render(). Both
access anchorError before its let binding is initialized, throwing
ReferenceError: Cannot access 'anchorError' before initialization.

Move all four let declarations (lastSnapshot, lastAttr, lastDelta,
anchorError) to the top of start(), before dialog.mount() and applyMode().
Function declarations are unaffected — they are hoisted regardless.

src/main.js

@@ -35,12 +35,29 @@ function findAnchorElement() {
 }
 
 function start() {
+  try {
     const store = new Store({
       storage: localStorage,
       onWarn: (m) => console.warn(m),
     });
     const prefs = store.getPrefs();
 
+    // State that applyMode() and render() may touch on first call.
+    // Declared up-front to avoid TDZ ReferenceError if applyMode()'s
+    // anchor-miss branch fires before the natural declaration point.
+    let lastSnapshot = null;
+    let lastAttr = null;
+    let lastDelta = 0;
+    let anchorError = null;
+
+    // One-time migration: dialog now defaults to bottom-left, so reset any
+    // previously-saved position from the bottom-right era.
+    if (prefs.pos && (prefs.pos.x !== 0 || prefs.pos.y !== 0)) {
+      console.info('[tat] resetting dialog position to new bottom-left default');
+      prefs.pos = { x: 0, y: 0 };
+      store.setPos(prefs.pos);
+    }
+
     const dialog = new Dialog({
       onTargetChange: (v) => {
         const attr = currentAttribute()?.attr;
@@ -60,11 +77,6 @@ function start() {
     dialog.mount({ initialMode: prefs.mode, initialPos: prefs.pos });
     applyMode();
 
-  let lastSnapshot = null;
-  let lastAttr = null;
-  let lastDelta = 0;
-  let anchorError = null;
-
     function snapshot() {
       const a = currentAttribute();
       if (!a) {
@@ -142,6 +154,9 @@ function start() {
       },
       onParseFail: (url) => console.warn('[tat] could not parse train response from', url),
     });
+  } catch (e) {
+    console.error('[tat] failed to start:', e);
+  }
 }
 
 if (location.hash === '#tat-test') {