WASD movement for the player

While W/A/S/D are held, the controlled creature gets a plain walk order every
engine tick toward its position plus the pressed screen direction, as the
mouse does while its button is held (every mouse event re-sends a walk to the
cursor point); releasing sends the target-less stop order of a released mouse
button. W/A/S/D key events are swallowed before the hotkeys see them; their
old actions move to G (action slot 3), V (pick up nearby) and K (save game
window) for now, configurable in [wasd].

docs/wasd.md: order format, measured mouse behaviour, hotkey map.
docs/todo.md: better pathfinder; final bindings for the moved hotkeys.
re::ConfigString for string settings.

Co-Authored-By: Claude Opus 5.5 (1M context) <noreply@anthropic.com>

docs/wasd.md

@@ -0,0 +1,60 @@
+# WASD movement (`src/mods/wasd.cpp`)
+
+## How the game moves the hero
+
+Movement is a creature order: `cEvent_creature` (vtable `0x88e95c`, 0x44
+bytes), command 4 = walk, sent with `cEngine::SendCreatureOrder` (`0x6170d0`,
+`(creature, event)`), which snaps a ground target to a walkable point and
+passes the order to `creature->vf18` (`cCreature::ReceiveOrder`, `0x52e400`).
+
+| Offset | Field |
+|---|---|
+| +4 | command (4 walk, 0x105 ...) |
+| +0x10 | target object id (attacks) |
+| +0x14 | 2: x, y are a ground point; 0: no target |
+| +0x18 / +0x1c | ground point (world units, same as creature +0x1c / +0x20) |
+| +0x20 | 1: re-aim while a mouse button is held; 2: skip target snapping |
+
+The controlled creature's object id is at `cEngine+0x13c`; objects come from
+`cObjectManager::GetObject` (`0x5fe060`, manager `*0xad3bc0`), cast with
+`__RTDynamicCast` to `cCreature`. Hero state: `+0xfc` action mode (2 while
+following a held mouse button), `+0x150` movement (1 walking, 2 arriving,
+0 standing).
+
+Mouse, measured with an order log:
+
+- click (`cEngine::HandleMouseButton` `0x617360`): one walk order to the
+  ground point, then engine flag `+0x54 |= 0x10` (button held);
+- while held: every mouse event re-sends a plain walk order (+0x20 = 0) to the
+  point under the cursor, dozens per tick; the hero stays in mode 2 and walks
+  smoothly. `cEngine::Tick` (`0x60f1d0`, 10 Hz) additionally sends a re-aim
+  order (+0x20 = 1) per tick after 0.4 s of walking;
+- release after > 0.5 s: a walk order without target (+0x14 = 0), which stops
+  the hero in place.
+
+## What the mod does
+
+Every `cEngine::Tick`, while W/A/S/D are held (and no text field has the
+focus, no mouse button is held): a plain walk order to hero position +
+direction x 300 world units (about a cursor's distance). Screen directions in
+world axes: up (-1,-1), down (1,1), left (-1,1), right (1,-1); combinations are
+summed and normalised. All keys released: the target-less stop order.
+
+Dead ends, for the record: re-aim orders (+0x20 = 1) on their own stop the
+hero after two orders; far targets (2000 units) are rejected or followed
+badly; targets near the stepwise-updated position make it arrive and stop.
+
+## Hotkeys
+
+Keys reach the game as `cEvent_key` (category 4; key at +6/+8, modifiers at
++0xa) through the kernel queue to `cEngine::ReceiveEvent` (`0x618130`), which
+offers them to `cUI_Manager::ReceiveEvent` (`0x757120`) first. Both compare
+`toupper(key)` (`0x84aa86`). The mod swallows W/A/S/D there (auto-repeat events
+would trigger the hotkeys) and rewrites the replacement keys into the old
+letters; the temporary bindings are listed in `docs/todo.md`.
+
+Hotkeys found: engine A (pick up nearby), P (pause), Q/W/E/R/B/Space
+(`cEngine::UseActionSlot`), ^ (console), Esc, Ctrl+B/F/X/Z (Z quicksave); UI
+manager C F H I L M N O S T (S save game window). Arrow keys in
+`cEngine::ScrollInput` (`0x610650`) walk object #2 or scroll the camera; not
+reachable in normal play.