Fix Feature 12 review findings F2–F8 on Regular grounding and onboarding

Grounding (F2–F5):
- Each ground_dinner job carries the dinner's new grounding_revision
  (migration 0010). Renaming a pending Regular raises the revision, and a
  job only grounds and writes a dinner still at its revision, so a queued
  original job no longer grounds the new name or decides the outcome.
- Background grounding keeps a method, minutes or difficulty a member saved
  while the Regular was pending, and fills only those left empty.
- Grounding by hand clears the pasted recipe_url, and link deduplication
  uses the source_url of the attached recipe, else the pending link.
- Archived dinners are not grounded: the job checks before any search,
  fetch or model call, and its final update requires an unarchived row.

Onboarding (F6, F7):
- Step 3 shows "Add Regulars" back to step 2 when the server refuses to
  finish with fewer than three Regulars.
- Common picks are hidden by a copy of harness Normalize/Similar, checked
  against the same shared cases as the Go code.

Docs (F8): ARCHITECTURE.md covers the three-Regular minimum, step-3
recovery, the grounding revision and the dedupe rules.

F1 was fixed in 1304487; its test now also asserts the old link is never
grounded and recipe_url stays cleared.

Maestro task 5037ff86-181d-448e-927b-c2fd2258a25d.

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

internal/db/models.go

@@ -51,24 +51,25 @@ type ChatSetting struct {
 }
 
 type Dinner struct {
-	ID              string
-	Name            string
-	NormalizedName  string
-	Status          string
-	Origin          string
-	Method          sql.NullString
-	MinutesTotal    sql.NullInt64
-	Difficulty      sql.NullString
-	Cuisine         sql.NullString
-	IsFavorite      int64
-	RecipeID        sql.NullString
-	PhotoID         sql.NullString
-	GroundingStatus string
-	UpdatedBy       sql.NullString
-	CreatedAt       string
-	UpdatedAt       string
-	RecipeUrl       sql.NullString
-	GroundingError  sql.NullString
+	ID                string
+	Name              string
+	NormalizedName    string
+	Status            string
+	Origin            string
+	Method            sql.NullString
+	MinutesTotal      sql.NullInt64
+	Difficulty        sql.NullString
+	Cuisine           sql.NullString
+	IsFavorite        int64
+	RecipeID          sql.NullString
+	PhotoID           sql.NullString
+	GroundingStatus   string
+	UpdatedBy         sql.NullString
+	CreatedAt         string
+	UpdatedAt         string
+	RecipeUrl         sql.NullString
+	GroundingError    sql.NullString
+	GroundingRevision int64
 }
 
 type HouseholdSetting struct {