fix: one password-failure message across every screen (closes #172)

A rejected password was reported three different ways depending on which screen
you were on, including the fragment "Wrong password." which is not a sentence.
All six decryptWithPassword call sites now show the same full sentence.

Strings only -- a wrong password still fails closed on every screen and still
resolves no pending approval.

A test pins the invariant per call site: each decryptWithPassword call is walked
out to its enclosing try and forward to that block's catch, and the prose shown
there must equal the canonical sentence. Per-file matching was not enough, since
a file with two call sites kept passing while one of them diverged.

src/popup/views/exportPrivkey.js

@@ -144,7 +144,7 @@ async function reveal() {
         $("export-privkey-flash").style.visibility = "hidden";
     } catch {
         if (!isCurrentReveal(generation)) return;
-        fail("That password is not correct. Please try again.");
+        fail("That password is incorrect. Please try again.");
     } finally {
         btn.disabled = false;
         btn.classList.remove("text-muted");