test(e2e): smoke spec — app loads and OTC sign-in succeeds via Mailpit

The first end-to-end smoke spec, run live against the Tier-1 stack
(§22 M3-0 Task 7). Drives the §6.2 email OTC sign-in: loads the app,
requests a code, reads it from Mailpit, verifies it, and asserts the
verify returns ok:true and sets the rfc_session cookie.

Supporting harness fixes:
- Makefile: add .PHONY so `make e2e` actually runs (the e2e/ directory
  was shadowing the target, making it a no-op).
- mailpit.js: guard the per-message detail fetch (if !full.ok continue)
  and scan the plain-text part before HTML so the \d{6} match can't
  latch onto a stray number.
- spec uses a unique per-run email to avoid the per-email request
  cooldown (OTC_REQUEST_COOLDOWN_SECONDS) on re-runs.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

e2e/lib/mailpit.js

@@ -10,9 +10,15 @@ export async function waitForLatestOtc(toAddress, { attempts = 20, delayMs = 500
       )
       if (msg) {
         const full = await fetch(`${MAILSINK}/api/v1/message/${msg.ID}`)
+        if (!full.ok) continue
         const body = await full.json()
-        const text = `${body.Text || ''} ${body.HTML || ''}`
-        const code = text.match(/\b(\d{6})\b/)
+        // Search the plain-text part first — the OTC mail is plain text
+        // (see backend/app/email_otc.py), and scanning Text before HTML
+        // keeps the \d{6} match from latching onto a stray number that a
+        // future HTML template might carry (style widths, year, etc.).
+        const text = body.Text || ''
+        const html = body.HTML || ''
+        const code = text.match(/\b(\d{6})\b/) || html.match(/\b(\d{6})\b/)
         if (code) return code[1]
       }
     }