fix(ai): pet order/home refactor — stop & post-combat behavior (#2459)

## Summary

Fixes two related pet-behavior bugs and the underlying design flaw behind both:

1. **Post-combat erratic** — after a pet killed its `all kill` target it milled around erratically at the kill site (or failed to return to the master) until the player issued `all follow`/`all stop`.
2. **`all stop` returns home** — a pet with a non-zero `Home` walked back toward that location on `all stop` (on ML; on non-ML the old `DoOrderStop` was a no-op, so the sighting there came from a residual `Stay`).

### Root cause

`ControlOrder` and the wild-creature `Home` field were overloaded to express several distinct ideas, mutated/read inconsistently across order transitions:

- `Home` doubled as the controlled-pet "stay anchor" (`HandleStayOrder` set `Home = Location`) but nothing cleared it when the pet left the staying state; `HandleStopOrder` was the only handler that never touched it.
- `DoOrderStop` had dropped RunUO's `Home = Location` re-anchor, so on ML it walked to a stale anchor.
- The post-combat fallback was a fragile `_lastPetOrder` hack in `DoOrderNone` that re-anchored a resumed `Stay` at the corpse.
- Controlled idle-wander bypassed the `CheckIdle()` rest gate that every non-controlled creature uses, so idling pets jittered every AI tick.

## Approach

Separate three concepts that were tangled together:

- **`ControlOrder`** — the active order (may be transient: Come/Attack/Drop).
- **Persistent command** (`PersistentOrder` ∈ `{None, Stay, Follow, Guard}`) — the standing directive a pet falls back to when a transient order completes. Runtime-only (not serialized; reset to `None` on load) and **derived from master proximity on login** (near → Follow, far → Stay).
- **Anchor** (`Home`) — a pure function of the persistent command, set only when that command changes (never on transient transitions or fallback-resume), so it can't go stale.

### Behavior

- **Stop** is resolved immediately from what the pet was doing: Attack/Come → resume the persistent command; Follow/Guard → cancel to idle where it stands; Stay → stay put.
- **Stay** holds its post (returns only if displaced, e.g. after a fight) — no shuffle.
- **Idle** (`None`) is a gentle wander routed through `CheckMove/CanMoveNow/CheckIdle`, so idling pets take the same 15–25s rest periods as other creatures, on both ML and non-ML.
- **Post-combat** the pet resumes its persistent command (a staying pet returns to its original post, not the corpse).
- **Release** without a spawner anchors where the pet stands instead of pathing to a stale anchor.

This restores the RunUO-intended behavior (verified against the RunUO reference) while fixing the ModernUO regressions.

## Tests

New `PetOrderTests` (13 deterministic xUnit tests) cover: anchor lifecycle, the full Stop truth table, report 1 (post-combat return to post), report 2 (no stale-anchor walk-home), frozen-Stay/gated-idle wiring, release fix, derive-on-login, and a non-ML spot-check. The subjective wander *feel* is covered by a manual-QA checklist in the implementation plan.

## Notes

- Engine project (`Projects/Server`) untouched; the one `BaseCreature.cs` change is the `ControlOrder` setter passing the previous order to `OnCurrentOrderChanged`.
- `DoOrderCome` keeps auto-converting to `Stay` on arrival, which under the new model cleanly means "come and hold near me."
- Commits in this PR are temporarily **unsigned** (the signing agent's passphrase cache expired mid-session); happy to re-sign / amend on request.

Projects/UOContent/Mobiles/AI/BaseAI/WalkRandomLogic.cs

@@ -38,6 +38,17 @@ public abstract partial class BaseAI
         }
     }
 
+    // Idle wander for controlled pets. Routes through the same CheckMove/CanMoveNow/CheckIdle
+    // gate that non-controlled DoActionWander uses, so idling pets take the gentle 15-25s
+    // CheckIdle rest periods instead of shuffling every AI tick.
+    public void WalkRandomIdle()
+    {
+        if (CheckMove() && CanMoveNow(out _) && !Mobile.CheckIdle())
+        {
+            WalkRandomInHome(3, 2, 1);
+        }
+    }
+
     public virtual void WalkRandomInHome(int chanceToNotMove, int chanceToDir, int steps)
     {
         if (Mobile.Deleted || Mobile.DisallowAllMoves)