Guard recipe repairs against same-normalized renames and member edits

F1-1: GroundDinner also compares the observed raw name, so renaming
"Grandma's stew" to "Easy Grandma's stew" (same normalized_name) while a
link is grounding is ErrGroundConflict, not attached to the renamed
dinner.

F1-2: A method, minutes_total or difficulty no longer as observed before
grounding is kept over the recipe's value, as GroundPendingDinner keeps
values a member set while a dinner was pending.

F2-1: Failing to record a grounded candidate or link on the dinner (or to
read it back after a rejected write) wraps ErrGroundFailed, so the API
logs reason=ground_failed with the dinner id, never the database error.

Maestro task 8741cedb-1849-4e3f-8d05-f5648c77c7ee.

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

internal/db/querier.go

@@ -70,10 +70,11 @@ type Querier interface {
 	// Records a dinner's grounding by hand (grounded or manual) and clears any
 	// grounding_error and pasted recipe_url: the recipe chosen replaces the
 	// link. It writes only an unarchived dinner still as it was observed
-	// before grounding (same normalized_name, grounding_status,
+	// before grounding (same name, normalized_name, grounding_status,
 	// grounding_revision and recipe_id), so a dinner renamed, archived or
 	// grounded some other way meanwhile is left as it is. That dinner, or an
-	// unknown id, returns sql.ErrNoRows.
+	// unknown id, returns sql.ErrNoRows. A method, minutes_total or difficulty
+	// no longer as observed is kept: a member edited it while it was grounding.
 	GroundDinner(ctx context.Context, arg GroundDinnerParams) (Dinner, error)
 	// Records the background grounding of an unarchived dinner still pending at
 	// the grounding_revision it was grounded for; a dinner grounded some other