Support both email and phone login

Auto-detect whether the user entered an email or phone number.
Email sends via Resend, phone sends via Twilio SMS. Users table
has nullable phone and email columns; verification_codes uses a
generic identifier field.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

templates/login.html

@@ -7,24 +7,25 @@
   <div class="event-tag">Account</div>
   <h1 class="event-title">Log in</h1>
   <p style="font-family:'DM Mono',monospace;font-size:0.8rem;color:#555;margin-top:8px;">
-    Enter your phone number to receive a login code.
+    Enter your email or phone number to receive a login code.
   </p>
 </div>
 
 <div class="claim-form-wrapper">
-  {{if eq .Step "phone"}}
+  {{if eq .Step "identify"}}
   <form method="POST" action="/login">
     <div class="form-row">
-      <label>Phone</label>
-      <input type="tel" name="phone" placeholder="(555) 123-4567" required autofocus>
+      <label>Email or phone</label>
+      <input type="text" name="identifier" placeholder="you@example.com or (555) 123-4567" required autofocus>
     </div>
     <button class="btn-submit" type="submit">Send code &#8599;</button>
   </form>
   {{else}}
   <form method="POST" action="/login/verify">
-    <input type="hidden" name="phone" value="{{.Phone}}">
+    <input type="hidden" name="identifier" value="{{.Identifier}}">
+    <input type="hidden" name="method" value="{{.Method}}">
     <p style="font-family:'DM Mono',monospace;font-size:0.78rem;color:#555;margin-bottom:16px;">
-      Code sent to <strong>{{.Phone}}</strong>
+      Code sent to <strong>{{.Identifier}}</strong>
     </p>
     {{if .Error}}
     <p style="color:#c44;font-size:0.85rem;margin-bottom:12px;">{{.Error}}</p>