feat: replace Bootstrap with custom CSS and add profile page

- Add self-hosted style.css replacing Bootstrap CDN dependency
- Add profile.html with tabbed view (account info, emails/aliases, API token)
- Refactor login handler to pass structured data to template instead of building HTML strings
- Add brand-name and brand-logo flags/env vars for UI customization
- Update CSP to allow brand logo domain and remove CDN references
- Update all templates to pass template vars to header/footer and use new CSS classes

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

static/lost.html

@@ -1,16 +1,19 @@
-{{template "header"}}
-  <h1 class="display-4">Forgot your password? <small class="text-muted">We'll send you a link by e-mail to reset it!</small></h1>
+{{template "header" .}}
+  <h1 class="page-title">Forgot your password?</h1>
+  <p class="page-subtitle">We'll send you a link by e-mail to reset it!</p>
 
   <form method="post" action="lost">
-    {{if .error}}<div class="alert alert-danger" role="alert">{{.error}}</div>{{end}}
+    {{if .error}}<div class="alert alert-error" role="alert">{{.error}}</div>{{end}}
     <input type="hidden" name="csrf_token" value="{{ .csrf_token }}">
-    <div class="form-group">
+    <div class="form-field">
       <input name="login" required="" class="form-control" id="input_0" type="text" placeholder="Login" autofocus>
     </div>
-    <div class="form-group">
+    <div class="form-field">
       <altcha-widget challengeurl="altcha-challenge"></altcha-widget>
     </div>
-    <button class="btn btn-primary" type="submit">Reset my password</button>
-    <a href="/change" class="btn btn-outline-success">Just want to change your password?</a>
+    <div class="btn-group">
+      <button class="btn btn-primary" type="submit">Reset my password</button>
+      <a href="/change" class="btn btn-secondary">Just want to change your password?</a>
+    </div>
   </form>
-{{template "footer"}}
+{{template "footer" .}}