refactor(collections): rule evaluators take the real row; both 45-field converter twins deleted

checkRulesAgainstBook/evaluateRule and the service's EvaluateRules
existed in two parallel universes: one over database.MediaItems (what
every query actually returns) and one over ListMediaItemsRow (what two
hand-written 45-field mediaItemsToListMediaItemsRow converters
produced — verbatim twins in the handler and the dashboard service,
with a URL-resolution side effect baked into a "converter"). The rule
fields (genre/series/author/language/publisher/copyright_year/tags)
all exist on MediaItems, so the evaluators now take the real row and
the converters, their three call-site loops, and the dead
ApplyAutoAssignRules entry point (zero callers) are gone.

The rules surface is wire-covered by the collections rules scenarios;
handlers+services suites and the full pin/H1/H3 battery green.

internal/services/statistics_service.go

@@ -561,9 +561,9 @@ type UsageItemStats struct {
 	Title       string  `json:"title"`
 	Author      string  `json:"author"`
 	CoverImage  string  `json:"cover_image_path"`
-	Seconds     float64 `json:"seconds"`  // audio duration (0 unless hours_mode)
-	PageCount   int     `json:"pages"`    // text pages (0 unless !hours_mode)
-	SizeBytes   int64   `json:"size"`     // always set, both modes
+	Seconds     float64 `json:"seconds"` // audio duration (0 unless hours_mode)
+	PageCount   int     `json:"pages"`   // text pages (0 unless !hours_mode)
+	SizeBytes   int64   `json:"size"`    // always set, both modes
 }
 
 // LibraryUsageStats is the whole tab payload for one scope: "" LibraryID
@@ -573,18 +573,18 @@ type UsageItemStats struct {
 // text pages. TotalSeconds/TotalPages both always carry their sums so
 // the client never has to infer.
 type LibraryUsageStats struct {
-	LibraryID      string            `json:"library_id"`
-	Items          int               `json:"items"`
-	Authors        int               `json:"authors"`
-	Narrators      int               `json:"narrators"`
-	TotalSizeBytes int64             `json:"total_size_bytes"`
-	TotalSeconds   int64             `json:"total_seconds"`
-	TotalPages     int               `json:"total_pages"`
-	HoursMode      bool              `json:"hours_mode"`
-	Genres         []NameCountStats  `json:"genres"`
-	AuthorsTop     []NameCountStats  `json:"top_authors"`
-	LongestItems   []UsageItemStats  `json:"longest_items"`
-	LargestItems   []UsageItemStats  `json:"largest_items"`
+	LibraryID      string           `json:"library_id"`
+	Items          int              `json:"items"`
+	Authors        int              `json:"authors"`
+	Narrators      int              `json:"narrators"`
+	TotalSizeBytes int64            `json:"total_size_bytes"`
+	TotalSeconds   int64            `json:"total_seconds"`
+	TotalPages     int              `json:"total_pages"`
+	HoursMode      bool             `json:"hours_mode"`
+	Genres         []NameCountStats `json:"genres"`
+	AuthorsTop     []NameCountStats `json:"top_authors"`
+	LongestItems   []UsageItemStats `json:"longest_items"`
+	LargestItems   []UsageItemStats `json:"largest_items"`
 }
 
 // LibraryUsage builds the /stats Library tab payload for one scope.