Grounding pipeline and recipe-search settings API

recipes.Grounder ties search, fetch/extract, Rank, the photo cache and
normalize_recipe together. Ground(ctx, dishName, query) reuses a stored
source_url among the top candidates without fetching, otherwise tries the
ranked recipes best first and stores the photo, recipe, ingredients and
steps in one transaction, returning Grounded{recipe_id, photo_id, method,
minutes_total, difficulty, source_url, site_name} or a typed
*ErrUngroundable listing every reason. GroundURL grounds a pasted URL the
same way; GroundMany grounds items 3 at a time with per-item results.

PhotoCache is split into DownloadPhoto (fetch, decode, size check, no
writes) and CachePhoto(ctx, tx, photo), which records the row in the
caller's transaction; RemovePhotoFiles cleans up after a rollback.

Migration 0007 adds photo_id, method, difficulty and minutes_total to
recipes, and api_key_last4 to recipe_search_settings. SearXNG is now
called at recipe_search_settings.base_url.

GET/PATCH /api/v1/settings/recipe-search (Brave key sealed with
secretbox, only api_key_set and api_key_last4 returned) and POST
/api/v1/settings/recipe-search/test (searches "chicken tikka masala",
returns the count, 409 not_configured or 502 search_failed).

Maestro task 53afd59c-6c35-4af7-904c-6c167d1ad69d.

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

internal/db/models.go

@@ -181,6 +181,10 @@ type Recipe struct {
 	FetchedAt    string
 	CreatedAt    string
 	UpdatedAt    string
+	PhotoID      sql.NullString
+	Method       sql.NullString
+	Difficulty   sql.NullString
+	MinutesTotal sql.NullInt64
 }
 
 type RecipeIngredient struct {
@@ -197,12 +201,13 @@ type RecipeIngredient struct {
 }
 
 type RecipeSearchSetting struct {
-	ID        int64
-	Provider  string
-	BaseUrl   sql.NullString
-	ApiKeyCt  []byte
-	CreatedAt string
-	UpdatedAt string
+	ID          int64
+	Provider    string
+	BaseUrl     sql.NullString
+	ApiKeyCt    []byte
+	CreatedAt   string
+	UpdatedAt   string
+	ApiKeyLast4 sql.NullString
 }
 
 type RecipeStep struct {