feat(admin): grant hints to a user's wallet from the console

Add an "Add hints" form on the admin user card that additively tops up a
player's hint wallet (1-100 per grant). The grant is raise-only by
construction (an additive UPDATE never lowers the balance) and stays correct
under a concurrent in-game spend; a per-grant cap bounds a fat-finger, since
the console can never reduce a wallet.

The in-game hint policy is unchanged and already correct: a game offers the
per-seat allowance plus the wallet, spending the allowance first and the
wallet only after (covered by TestHintPolicy).

backend/internal/adminconsole/templates/pages/user_detail.gohtml

@@ -21,6 +21,10 @@
 <button type="submit">Clear high-rate flag</button>
 </form>
 {{end}}
+<form class="form" method="post" action="/_gm/users/{{.ID}}/grant-hints">
+<label>Add hints <input type="number" name="amount" min="1" max="{{.HintGrantMax}}" value="1"></label>
+<button type="submit">Grant</button>
+</form>
 </section>
 <section class="panel"><h2>Statistics</h2>
 {{if .HasStats}}

backend/internal/adminconsole/views.go

@@ -125,13 +125,16 @@ type UserDetailView struct {
 	// empty for an unflagged account; the card shows it with the Clear action.
 	FlaggedHighRateAt string
 	HintBalance       int
-	CreatedAt         string
-	HasStats          bool
-	Stats             StatsRow
-	Identities        []IdentityRow
-	Games             []GameRow
-	TelegramID        string
-	ConnectorEnabled  bool
+	// HintGrantMax is the per-grant cap the operator's "add hints" form enforces (it mirrors the
+	// server's maxHintGrant), passed through so the policy value lives in one place.
+	HintGrantMax     int
+	CreatedAt        string
+	HasStats         bool
+	Stats            StatsRow
+	Identities       []IdentityRow
+	Games            []GameRow
+	TelegramID       string
+	ConnectorEnabled bool
 	// MoveChart is the pre-rendered inline SVG of the account's per-move-number think
 	// time (min/mean/max), empty when the account has no timed move.
 	MoveChart template.HTML