fix(layout): mobile UX cleanup + interest-stage legend popover

Mobile UX:
- Hide ColumnPicker on `< sm` viewports (cards, no columns to toggle).
- Hide kanban toggle in interest list on mobile and snap viewMode back
  to 'table' if the persisted choice was 'board'.
- Drop dead "Inbox" link from the More-sheet (email/IMAP feature is
  deferred per sidebar.tsx note).
- Repoint Notifications nav from `/notifications` (no page.tsx — 404)
  to `/notifications/preferences` and re-label as "Notification
  preferences" (the bell stays the surface for actual notifications).
- Hide Website Analytics on both desktop sidebar and mobile More-sheet
  when Umami isn't configured for the port (`useUmamiActive()`).

Interests:
- New `<StageLegend>` popover button in the filter row decodes the
  card stripe colours to pipeline stage names, kept in sync with
  `STAGE_DOT` automatically.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

src/components/interests/interest-list.tsx

@@ -1,6 +1,6 @@
 'use client';
 
-import { useState } from 'react';
+import { useEffect, useState } from 'react';
 import { useParams } from 'next/navigation';
 import {
   Plus,
@@ -35,6 +35,7 @@ import { ColumnPicker } from '@/components/shared/column-picker';
 import { SaveViewDialog } from '@/components/shared/save-view-dialog';
 import { useTablePreferences } from '@/hooks/use-table-preferences';
 import { InterestCard } from '@/components/interests/interest-card';
+import { StageLegend } from '@/components/interests/stage-legend';
 import { TagPicker } from '@/components/shared/tag-picker';
 import {
   Dialog,
@@ -63,6 +64,13 @@ export function InterestList() {
   const queryClient = useQueryClient();
   const { viewMode, setViewMode } = usePipelineStore();
 
+  // Force the list view at mobile widths even when the user previously
+  // toggled the kanban from desktop — the board is desktop-only.
+  useEffect(() => {
+    if (typeof window === 'undefined') return;
+    if (viewMode === 'board' && window.innerWidth < 640) setViewMode('table');
+  }, [viewMode, setViewMode]);
+
   const [createOpen, setCreateOpen] = useState(false);
   const [editInterest, setEditInterest] = useState<InterestRow | null>(null);
   const [archiveInterest, setArchiveInterest] = useState<InterestRow | null>(null);
@@ -157,7 +165,10 @@ export function InterestList() {
         variant="gradient"
         actions={
           <div className="flex items-center gap-2">
-            <div className="flex items-center border rounded-md overflow-hidden">
+            {/* Kanban view is desktop-only — mobile drops the toggle and
+                falls back to the list/cards view (the board's column
+                horizontal-scroll model is unusable at phone widths). */}
+            <div className="hidden sm:flex items-center border rounded-md overflow-hidden">
               <Button
                 size="sm"
                 variant={viewMode === 'table' ? 'default' : 'ghost'}
@@ -234,6 +245,7 @@ export function InterestList() {
             />
           </>
         ) : null}
+        <StageLegend />
       </div>
 
       <SaveViewDialog