panel-redesign: paths follow the menu; Account and Server settings split

Stage 1, step 3 (plan § Routes). BREAKING: every panel URL changes and the
old paths are removed without redirects.

Routes (web.go)
  - /status -> /overview; /domains -> /outbound/domains with the domain's
    settings actions under .../settings/ (reports, ratelimit, export);
    /deliveries -> /outbound/log; /mail-queue -> /outbound/queue; /dmarc ->
    /outbound/dmarc; /inbound -> /inbound/domains; /system-log ->
    /server/log; /backup -> /server/backup (import under it); /users ->
    /server/users; recheck and reload under /server/health/.
  - One fragment name: <page>/fragment everywhere.
  - Everything under /server/ is registered through server(), which wraps
    the handler in globalOnly: the subtree is guarded once, where a new
    route cannot forget it. Handlers keep their own requireGlobal.
  - GET / leads to /overview, /outbound/domains or /inbound/domains.
  - The /account -> /settings redirect is gone with /settings.

Account and Server > Settings
  - handlers_account.go: GET /account and three POSTs - profile (username,
    e-mail; no password asked, as designed), password (current password,
    rate-limited like a sign-in, signs out other sessions), dmarc (the
    user's default: hosted / account / custom / none, each validated).
    This replaces step 1's bridge through the old Settings form.
  - handlers_settings.go is the instance's page only: log retention and the
    read-only rate limits, global role.
  - One legacy template serves both pages by a flag until stage 2 gives each
    its own: a new legacy page cannot be added to the ratchet.

Still to come inside stage 1, and why @routes stays on the ratchet:
  - step 4: the application routes (one POST, under the domain);
  - step 5: GET /server/health.
With @routes removed by hand TestRoutesFollowNavigation reports exactly
those and nothing else - no template links to a path the router lacks.

Old templates, tests and the e2e client are retargeted. The e2e module was
edited but not run here (no Docker, and its dependency could not be
downloaded on this machine).

Tests: Account (page, profile, password, DMARC default in every mode, a
domain administrator's own row only), Server settings (saved without a
password, range, global only), the /server/ subtree answered 404 by the
router for a domain administrator with All on both lists and for no
principal.

go test ./...  green except the two Windows-only failures in internal/domain
and internal/logtail.

Roadmap 13/27.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

internal/web/view/templates/inbound_domain.html

@@ -3,7 +3,7 @@
 {{define "content"}}
 <h1>{{.Domain.Name}}</h1>
 
-{{template "back_link" (back "/inbound" "All inbound domains")}}
+{{template "back_link" (back "/inbound/domains" "All inbound domains")}}
 
 {{if .Flash}}<div class="flash">{{.Flash}}</div>{{end}}
 
@@ -34,7 +34,7 @@
   {{else}}
   <p class="error">{{.MX.Detail}}</p>
   {{end}}
-  <form method="post" action="/inbound/{{.Domain.ID}}/dns-recheck">
+  <form method="post" action="/inbound/domains/{{.Domain.ID}}/dns-recheck">
     <button type="submit">Re-check</button>
   </form>
 </div>
@@ -43,7 +43,7 @@
   <div class="card">
     <h2>Upstream</h2>
     <p class="muted">Where accepted mail is handed off. Not a mailbox.</p>
-    <form method="post" action="/inbound/{{.Domain.ID}}/upstream">
+    <form method="post" action="/inbound/domains/{{.Domain.ID}}/upstream">
       <label for="host">Host</label>
       <input id="host" name="host" type="text" value="{{.Domain.Host}}"
              autocomplete="off" autocapitalize="none" spellcheck="false" required>
@@ -89,7 +89,7 @@
     <h2>Valid recipients</h2>
     <p class="muted">Who this domain accepts on port 25. Same idea as an
     application's address mode: a list, or any address at the domain.</p>
-    <form method="post" action="/inbound/{{.Domain.ID}}/recipients">
+    <form method="post" action="/inbound/domains/{{.Domain.ID}}/recipients">
       <label for="recipient_mode">Who to accept</label>
       <select id="recipient_mode" name="recipient_mode" data-list-mode="list">
         <option value="list" {{if eq .Domain.RecipientMode "list"}}selected{{end}}>Listed addresses only</option>
@@ -112,7 +112,7 @@
     <h2>Danger zone</h2>
     <p class="muted">Stops accepting mail for this domain. Does not touch
     outbound sending domains.</p>
-    {{if .IsGlobal}}<p><a class="danger" href="/inbound/{{.Domain.ID}}/delete">Delete inbound domain</a></p>{{end}}
+    {{if .IsGlobal}}<p><a class="danger" href="/inbound/domains/{{.Domain.ID}}/delete">Delete inbound domain</a></p>{{end}}
   </div>
 </div>
 {{end}}