Seed player_meta on auto-migration to prevent player_meta-less stragglers

The !setup confirm path seeds the canonical player_meta row (commit
667f87f), but the auto-migration path (ensureDnDCharacterForCombat) writes
a confirmed dnd_character without touching the legacy layer. Commands that
trigger it — !rest, !cast, !abilities, !skills — derive the adventure char
via a bare loadAdvCharacter that is nil when player_meta is absent, and
autoBuildCharacter tolerates a nil char. So a brand-new player whose
first-ever adventure action is one of those gets a confirmed character with
no player_meta, which then fails every legacy-layer command (expeditions,
arena, world boss, town, duels) with "sql: no rows" — the same state
@camcast was found in.

Fix: ensurePlayerMetaSeed guarantees the seed row (+ tier-0 equipment)
exists at the fresh auto-migration point. Conditional on player_meta being
absent, so it's idempotent and never duplicates a legacy player's gear
(createAdvCharacter's equipment insert has no conflict guard).

Regression tests cover both the straggler repro (first-ever !rest seeds
player_meta + loads cleanly) and idempotency (no equipment duplication).

Claude-Session: https://claude.ai/code/session_017mEwUmmS7aQTP2NQXj6rUa

internal/plugin/dnd_combat.go

@@ -1,6 +1,7 @@
 package plugin
 
 import (
+	"fmt"
 	"log/slog"
 	"time"
 
@@ -305,6 +306,13 @@ func ensureDnDCharacterForCombat(userID id.UserID, char *AdventureCharacter) (*D
 	c := autoBuildCharacter(userID, char)
 	c.AutoMigrated = true
 	c.PendingSetup = false
+	// Seed the canonical player_meta row before handing back a confirmed
+	// character. Auto-migration otherwise mints a player_meta-less character
+	// (the camcast straggler) that fails every legacy-layer command with
+	// "sql: no rows". No-op for legacy players who already have the row.
+	if err := ensurePlayerMetaSeed(userID); err != nil {
+		return nil, false, fmt.Errorf("seed player_meta: %w", err)
+	}
 	if err := SaveDnDCharacter(c); err != nil {
 		return nil, false, err
 	}