feat: derive the Running bit from the step pace and fix step-pacing bursts (#2599)

Stacked on #2594. Fixes jerky creature movement (lich / Fast-bucket melee chases) by choosing the client animation flag from the actual step pace instead of a caller-supplied `run` argument, and fixes three step-pacing defects in the move budget found while verifying it with paired server/client traces.

### Why

The `Direction.Running` bit does nothing for creatures server-side (`Mobile.OnMove` reads it only for the player throttle and stealth reveal). Its whole effect is on the client, which animates each step over a fixed time selected by that bit: walk 400 ms / run 200 ms on foot, 200 / 100 ms mounted. ClassicUO queues up to 5 steps and *drops* the sixth, so a creature stepping every 300 ms while flagged as walking backs the queue up until it snaps forward — the observed jerk.

The `run` argument never carried the one fact that matters (the step interval). RunUO passed `true` in combat / `false` for pets and gated it on `dist > 5`; #2271 flipped every combat site to `false`; pets passed `currentDistance > 2`. None of that is a coherent signal.

### What

**Pace-derived run flag**
- `BaseAI.ShouldRun()`: run iff the effective step delay (move clock + badly-hurt inflation) is shorter than `Movement.WalkFootDelay` / `WalkMountDelay` (mounted or flying) — with a continuity rule: an *isolated* step (taken after standing at least a walk interval) goes out as a walk, because the client renders each step alone and a lone run-flagged step is a 200 ms dart. Only a continuing cadence flags run; a true sprinter (pace under the run interpolation) always runs, since a walk-rendered first step would flood the client's 5-step queue. This reproduces RunUO's close-in feel (its `dist > 5` gate) from first principles.
- `DoMoveImpl` stamps the bit; it is the single place the flag is set.
- `run` removed from `MoveTo`, `WalkMobileRange`, `ApproachTarget`, `MoveToPoint`, `MoveToWithGroup`, `MoveToWithCollisionAvoidance`, the move intent, and `PathFollower.Follow`. All 35 call sites updated. **API change** for custom scripts — documented in the RunUO migration docs (`09-items-mobiles-creatures.md`, `11-api-reference.md`) and `content-patterns.md` § Creature Speeds.

**Move-budget pacing fixes** (each confirmed by UTC-aligned server/client step traces)
- A stall no longer banks catch-up steps: the budget's snap-to-now released up to three steps in ~300 ms when a creature resumed chasing after standing beside its target — rendered as a teleport.
- Debt accrual removed entirely: a step landing sub-period late (think-grid vs budget misalignment during reactive mirroring) kept the remainder and fired a follow-up ~100 ms later — a dart pair. `ConsumeMoveBudget` now paces every step from when it was actually taken; in continuous pursuit the move-wake lands within wheel resolution of the deadline, so the cost is single-digit-ms drift.
- Net effect: a creature can never step faster than its pace, verified across a full chase session (zero sub-pace steps; metronomic 350 ms cadence for a 0.3 s lich).

- Test fixture now runs `Movement.Configure()` (the walk delays were 0 in tests).

### Accepted trade-off

Animal (LOW group) bodies without a run animation slide on their stand frames when flagged as running. Most are slow enough to stay flagged as walking; the client-side fallback is in ClassicUO/ClassicUO#1930.

### Tests

`RunFlagTests`: foot thresholds (0.3 / 0.125 run; 0.4 / 0.45 / 1.05 walk), flying uses the mount threshold, badly-hurt inflation flips a 0.35 s creature back to walk, a real `DoMove` stamps the bit, isolated steps drop to walk (sprinters keep running), a stall restarts the cadence with no banked steps, and a late step earns no quicker follow-up. Full suite: 837 Server + 747 UOContent green.

dev-docs/runuo-migration-docs/09-items-mobiles-creatures.md

@@ -474,6 +474,29 @@ The extra parameters (RangePerception, RangeFight, ActiveSpeed, PassiveSpeed) ha
 | `Name = "a creature"` in constructor | `public override string DefaultName => "a creature";` |
 | `get { return value; }` | `=> value;` expression-bodied |
 
+## AI Movement: No `run` Argument
+
+RunUO's movement calls took a `run` flag that callers set inconsistently (`true` in
+combat, `false` for pets, gated by `dist > 5` inside `MoveTo`). The flag only selects the
+client's per-step animation time, so ModernUO derives it from the creature's step pace
+(`BaseAI.ShouldRun`) and the parameter is gone:
+
+```csharp
+// RunUO
+MoveTo(combatant, true, m_Mobile.RangeFight);
+WalkMobileRange(m_Mobile.ControlMaster, 1, false, 0, 1);
+
+// ModernUO
+MoveTo(combatant, Mobile.RangeFight);
+WalkMobileRange(Mobile.ControlMaster, 1, 0, 1);
+```
+
+`ApproachTarget`, `MoveToPoint` and `PathFollower.Follow` lose the argument the same way.
+To make a creature run, make it fast (`SetMoveSpeed` / `npc-speeds.json`), not flagged.
+An isolated step (after the creature stood for at least a walk interval) goes out as a
+walk regardless of pace — only a continuing cadence, or a pace faster than the run
+interpolation, flags run.
+
 ## Item Name Changes
 
 ```csharp

dev-docs/runuo-migration-docs/11-api-reference.md

@@ -130,6 +130,9 @@ Alphabetical by RunUO API name. Use Ctrl+F / Cmd+F to search.
 | `writer.WriteEncodedInt(value)` | `writer.WriteEncodedInt(value)` | Same |
 | `InvalidateProperties()` | `InvalidateProperties()` | Same, or use `[InvalidateProperties]` |
 | `this.MarkDirty()` | `this.MarkDirty()` | NEW — required in custom setters |
+| `MoveTo(m, run, range)` | `MoveTo(m, range)` | `run` removed; the Running bit is derived from the step pace (`BaseAI.ShouldRun`) |
+| `WalkMobileRange(m, steps, run, min, max)` | `WalkMobileRange(m, steps, min, max)` | Same |
+| `PathFollower.Follow(run, range)` | `Follow(range)` | Same |
 
 ## Networking