PC controls: keyboard pan/zoom, Tab cycle, Escape stack, right-click deselect

Adds full PC keyboard+mouse support on top of existing touch controls. Touch
paths untouched. All input goes through named actions in project.godot.

Bindings:
- WASD / arrows: camera pan (speed scales with zoom)
- = / -: keyboard zoom in/out
- C / Home: center on selected pawn
- Tab / Shift+Tab: cycle through pawns (pans camera to selection)
- B / L / P / ,: toggle BuildDrawer / AlertsLog / WorkPriorityMatrix / Settings
- Escape: cancel active designation tool > close topmost panel > deselect pawn
- Right-click: cancel active tool or deselect pawn (RTS convention)
- F: speed_cycle (action restored; handler still TODO)
- pawn_prev action removed; Shift+Tab read via event.shift_pressed inline

Escape priority enforced by Designation._input running before _unhandled_input
plus each panel consuming its own cancel action when visible.

Also fixes a pre-existing pre-Phase-17 bug: WorkPriorityMatrix, AlertsLog,
StorytellerModal, LoadMenu, and SettingsMenu had MOUSE_FILTER_STOP Controls
(Backdrop / Dim) that remained input-active when the panel was "closed" —
their open/close paths only toggled _root.visible / _panel.visible, never
CanvasLayer.visible. World mouse events (right-click deselect, left-click
pawn-select) were silently eaten. Now each _set_visible / open / close
toggles self.visible (the CanvasLayer) so input dispatch shuts off properly.

Verified end-to-end via MCP runtime: WASD pan, zoom keys, Tab+Shift+Tab
cycle, B-open + Escape-close, right-click deselect, left-click pawn-select
all working in sequence with no input bleed.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

scenes/ui/build_drawer.gd

@@ -371,6 +371,21 @@ func _on_cancel_pressed() -> void:
 	Audit.log("build_drawer", "tool cancelled")
 
 
+# ── keyboard input ───────────────────────────────────────────────────────────
+
+func _unhandled_input(event: InputEvent) -> void:
+	# B — toggle the build drawer.
+	if event.is_action_pressed("open_build"):
+		toggle()
+		get_viewport().set_input_as_handled()
+		return
+	# Escape — close if open (panel Escape runs before Selection deselect).
+	if event.is_action_pressed("cancel") and _open:
+		close()
+		get_viewport().set_input_as_handled()
+		return
+
+
 # ── helpers — visibility ─────────────────────────────────────────────────────
 
 func _set_panel_visible(v: bool) -> void: