feat(mystery): /mystery route + CRT bezel + theme scaffold

src/ui/terminal.ts

@@ -0,0 +1,10 @@
+// Stub. Replaced in Task 10 with the full terminal implementation.
+console.info('[halfstreet] terminal placeholder loaded')
+
+const transcript = document.querySelector<HTMLDivElement>('[data-mystery-transcript]')
+if (transcript) {
+  const line = document.createElement('div')
+  line.className = 'narration'
+  line.textContent = 'Terminal scaffold loaded. Type wiring lands in the next task.'
+  transcript.appendChild(line)
+}