feat: private accounts, explore/people merge, meal-plan fixes, i18n and theme cleanup

- Private accounts: users.isPrivate hides a user from search and their
  recipes from search/trending/for-you discovery surfaces (follow-aware
  where the route already has session context, blanket exclusion where it
  doesn't); existing followers and direct links are unaffected, no
  follow-request approval flow was built (explicit scope limit)
- Merged /people into the Explore tab (tab=people query param); the old
  standalone route now redirects there
- "Get Ideas" vs "Surprise Me" were doing the same empty-prompt call;
  Surprise Me now injects a real random constraint (5-ingredient, one-pot,
  etc.), matching the existing pattern in the AI recipe-generate dialog
- Meal-plan day cells now link to their recipe (was dead text) and gained
  a one-click "mark as cooked" action
- Theme toggle is now a real three-way light/dark/system control instead
  of a binary flip
- Nutrition goals form had zero i18n wiring; fully localized now

New migration 0027 (users.is_private) generated, left unapplied like the
others. Verified with typecheck, lint, and a clean --no-cache docker build.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

apps/web/messages/en.json

@@ -19,7 +19,8 @@
     "notifications": "Notifications",
     "viewProfile": "View profile",
     "lightMode": "Light mode",
-    "darkMode": "Dark mode"
+    "darkMode": "Dark mode",
+    "systemMode": "System"
   },
   "notifications": {
     "title": "Notifications",
@@ -305,7 +306,19 @@
     "nutritionGoals": {
       "title": "Daily Nutrition Goals",
       "description": "Set your daily targets. These are shown as progress bars on your meal plan.",
-      "viewDiaryCta": "View nutrition diary"
+      "viewDiaryCta": "View nutrition diary",
+      "caloriesLabel": "Calories (kcal/day)",
+      "proteinLabel": "Protein (g/day)",
+      "carbsLabel": "Carbs (g/day)",
+      "fatLabel": "Fat (g/day)",
+      "caloriesPlaceholder": "e.g. 2000",
+      "proteinPlaceholder": "e.g. 50",
+      "carbsPlaceholder": "e.g. 250",
+      "fatPlaceholder": "e.g. 70",
+      "saveButton": "Save goals",
+      "saving": "Saving...",
+      "saveSuccess": "Nutrition goals saved",
+      "saveError": "Failed to save nutrition goals"
     },
     "webhooksPage": {
       "title": "Webhooks",
@@ -423,6 +436,8 @@
   },
   "explore": {
     "title": "Explore",
+    "tabRecipes": "Recipes",
+    "tabPeople": "People",
     "searchPlaceholder": "Search public recipes…",
     "maxMinutes": "Max minutes",
     "aiSearchPlaceholder": "e.g. quick weeknight dinners, Italian comfort food…",
@@ -689,7 +704,10 @@
     "listCreate": "Create",
     "pickRecipe": "Pick recipe",
     "addEntry": "+ Add",
-    "removeEntry": "Remove meal"
+    "removeEntry": "Remove meal",
+    "markCooked": "Mark as cooked",
+    "markCookedSuccess": "Marked as cooked",
+    "markCookedFailed": "Failed to mark as cooked"
   },
   "pantry": {
     "title": "Pantry",
@@ -1026,7 +1044,9 @@
     "publicBioPlaceholder": "Tell other cooks about yourself…",
     "privateBio": "AI context (private)",
     "privateBioDescription": "Never shown publicly. Injected into AI prompts to personalise suggestions — add your dietary preferences, kitchen equipment, cooking skill level, allergies, etc.",
-    "privateBioPlaceholder": "e.g. I'm vegetarian, have a stand mixer and an air fryer, intermediate cook, allergic to tree nuts, prefer Mediterranean flavours…"
+    "privateBioPlaceholder": "e.g. I'm vegetarian, have a stand mixer and an air fryer, intermediate cook, allergic to tree nuts, prefer Mediterranean flavours…",
+    "privateAccount": "Private account",
+    "privateAccountDescription": "When on, your profile and recipes won't appear in search or discovery (Explore, Trending, For You). People who already follow you keep seeing your recipes."
   },
   "profilePage": {
     "tabRecipes": "Recipes",