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>

docs/ARCHITECTURE.md

@@ -254,10 +254,12 @@ automatic** (D-021).
   `dinner_archived`. A candidate or link is written only if the dinner is
   still as it was before grounding began: one renamed or grounded some
   other way meanwhile is 409 `ground_conflict`, and one archived meanwhile
-  409 `dinner_archived`, either leaving the dinner unchanged. Any other
-  failure grounding a candidate or link is 500, logged with a fixed reason
-  and the dinner id only — never the link, which can carry a personal
-  token, or dependency error text.
+  409 `dinner_archived`, either leaving the dinner unchanged. A method,
+  minutes or difficulty a member edits meanwhile is kept over the recipe's.
+  Any other failure grounding a candidate or link, or recording it on the
+  dinner, is 500, logged with a fixed reason and the dinner id only —
+  never the link, which can carry a personal token, or dependency error
+  text.
 - `/health` — liveness.
 - Everything else serves the embedded PWA with SPA fallback.