feat: 404 log and report endpoint

- POST /_seo/api/v1/notfound with the golem15.seo.notfound_token bearer
  (constant-time, off when unset), URL and referer caps, a row cap with
  an hourly warning, throttle bucket seo-notfound
- golem15.seo.notfound list by hits with Resolved rows, a preview with the
  resolved hint, a prompted 301 and a 410 record action, a bulk 410 that
  refuses a selection with a covered address
- every /_seo/api/v1 answer carries X-Robots-Tag: noindex

controllers/notfound/_hint.htm

@@ -0,0 +1,5 @@
+{{- with .Data.Text -}}
+<div class="summer-callout" role="status">
+<p class="summer-callout__text">{{ . }}</p>
+</div>
+{{- end -}}

controllers/notfound/config_filter.yaml

@@ -0,0 +1,11 @@
+# 404 log filters (UI-SPEC C9): open or resolved, and the last hit.
+scopes:
+    status:
+        label: golem15.seo::lang.notfound.filter_status
+        modelClass: Golem15\SEO\Models\NotFound
+        nameFrom: url
+        scope: FilterNotFoundStatus
+    last_hit:
+        label: golem15.seo::lang.notfound.last_hit
+        type: daterange
+        column: last_hit

controllers/notfound/config_form.yaml

@@ -0,0 +1,14 @@
+# 404 log preview (UI-SPEC C9): read-only, the resolved hint above the card
+# and the two actions that apply while the entry is open.
+name: golem15.seo::lang.notfound.name
+form: ~/plugins/golem15/seo/models/notfound/fields.yaml
+modelClass: Golem15\SEO\Models\NotFound
+defaultRedirect: golem15/seo/notfound
+
+preview:
+    headerPartial: hint
+
+recordActions: [redirect, gone]
+
+messages:
+    preview: golem15.seo::lang.notfound.preview

controllers/notfound/config_list.yaml

@@ -0,0 +1,25 @@
+# 404 log (UI-SPEC C9): most hits first, resolved entries badged, no create.
+list: ~/plugins/golem15/seo/models/notfound/columns.yaml
+modelClass: Golem15\SEO\Models\NotFound
+title: golem15.seo::lang.notfound.list_title
+recordUrl: golem15/seo/notfound/preview/:id
+noRecordsMessage: golem15.seo::lang.notfound.list_empty
+recordsPerPage: 50
+showCheckboxes: true
+showSetup: true
+filter: config_filter.yaml
+bulkActions: [gone]
+
+defaultSort:
+    column: hits
+    direction: desc
+
+toolbar:
+    buttons: [delete]
+    search:
+        prompt: backend::lang.list.search_prompt
+
+messages:
+    empty: golem15.seo::lang.notfound.list_empty
+    deleteConfirm: golem15.seo::lang.notfound.delete_selected_confirm
+    rowStateDisabled: golem15.seo::lang.notfound.state_resolved