Expedition autopilot Phase 1: !explore / !expedition run

Adds an autopilot loop that walks rooms automatically until a
natural or threshold interrupt fires.

- New !explore (top-level alias) and !expedition run subcommand
  driven by expeditionCmdRun in dnd_expedition_cmd.go.
- advanceOnce extracted from zoneCmdAdvance so the autopilot and
  the manual !zone advance path share one room-step implementation.
- Stop reasons: fork, elite/boss doorway, death, complete,
  active-combat block, HP <= 30%, SU < 1 day's burn, 6-room cap.
- Trash combat continues to auto-resolve inside resolveCombatRoom;
  no changes there.
- TestAutopilotFooter_Reasons covers the pure stop-reason logic;
  preflight + walk tests skip without the prod DB, matching the
  existing setupAuditTestDB pattern.

Phase 2 (auto-harvest) and Phase 3 (real-time ticking) deferred.

internal/plugin/adventure.go

@@ -170,6 +170,7 @@ func (p *AdventurePlugin) Commands() []CommandDef {
 		{Name: "commune", Description: "Commune with spiritual energy in your current expedition region (Cleric primary)", Usage: "!commune", Category: "Games"},
 		{Name: "fish", Description: "Fish in your current expedition region (DEX / Sleight of Hand; water zones only)", Usage: "!fish", Category: "Games"},
 		{Name: "resources", Description: "List harvestable resources in your current expedition region", Usage: "!resources", Category: "Games"},
+		{Name: "explore", Description: "Autopilot: walk through expedition rooms until something needs your attention (fork, elite/boss, low HP/supplies)", Usage: "!explore", Category: "Games"},
 		{Name: "sell", Description: "Sell harvested materials/fish/items to Thom Krooke (post-expedition; CHA Persuasion DC 17 = +15%)", Usage: "!sell [list|all|<item>]", Category: "Games"},
 		{Name: "craft", Description: "Craft a discovered recipe at Thom Krooke (consumes ingredients)", Usage: "!craft [list|<recipe>]", Category: "Games"},
 		{Name: "lore", Description: "Dig through Thom Krooke's lore stacks for an undiscovered recipe (INT/Arcana DC 15)", Usage: "!lore", Category: "Games"},
@@ -354,6 +355,9 @@ func (p *AdventurePlugin) OnMessage(ctx MessageContext) error {
 	if p.IsCommand(ctx.Body, "map") {
 		return p.handleExpeditionMapCmd(ctx, p.GetArgs(ctx.Body, "map"))
 	}
+	if p.IsCommand(ctx.Body, "explore") {
+		return p.expeditionCmdRun(ctx)
+	}
 	if p.IsCommand(ctx.Body, "forage") {
 		return p.handleHarvestCmd(ctx, HarvestForage)
 	}