sow no longer needs grain + add crop zone paint tools

Bug: pawns weren't replanting. _find_sow required a TYPE_GRAIN item
as seed, but Millstone's flour bill (FOREVER) consumed all grain
before sow could claim it. With CookingProvider now priority 6, grain
contention is fatal — TILLED crops sit forever.

Fix: removed the grain requirement. Sow is now Rimworld-style — the
designation triggers work; no input is consumed. _find_sow returns a
2-toil job (walk → interact). Crop.on_sow_tick just flips stage to
SOWN.

Feature: 4 new paint tools in BuildDrawer's new "Farm" section column
— TOOL_PAINT_CROP_WHEAT/POTATO/CORN/STRAWBERRY. Painting a grass
tile spawns a TILLED Crop entity that pawns then sow. World rejects
non-grass tiles, occupied tiles, and non-walkable terrain. 9 new
string keys, kind-specific thumbnail draws (gold/tan/yellow/red).

MCP verified: 12 forced-TILLED crops fully cycled TILLED → SOWN →
growth → READY within ~3000 ticks. Paint tool spawned wheat crop at
(35, 30); wall tile at (44, 23) correctly rejected.

Followup smell: cancelling a designation on a player-painted crop
will queue_free even if grown — Crop has no can_complete. Future
guard could skip crops past TILLED.

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

scenes/ai/plant_provider.gd

@@ -12,17 +12,10 @@ class_name PlantProvider extends WorkProvider
 ## Harvest Job (two toils):
 ##   walk_to(crop.tile) → interact(crop.get_path(), "on_harvest_tick")
 ##
-## Sow Job (four toils):
-##   walk_to(grain_item.tile) → pickup → walk_to(crop.tile)
-##       → interact(crop.get_path(), "on_sow_tick")
-##   The grain item is consumed by the INTERACT completion (on_sow_tick does
-##   the stage transition; the pawn's carried item is cleared by the provider
-##   by queuing a DROP toil after interact, or — simpler — on_sow_tick itself
-##   does not free the item, so we add a consume step here).
-##
-## Seed item: Item.TYPE_GRAIN (&"grain") — universal MVP seed for all crop kinds.
-##   Wheat/corn already produce grain on harvest. Potato/strawberry accept grain
-##   as seed in the same way (MVP simplification noted in design.md).
+## Sow Job (two toils — no seed cost, Rimworld-style):
+##   walk_to(crop.tile) → interact(crop.get_path(), "on_sow_tick")
+##   The designation alone triggers work; no grain is consumed.  on_sow_tick()
+##   flips the crop from TILLED → SOWN so growth begins on the next sim tick.
 ##
 ## The INTERACT toil calls the action method once per sim tick.  Both actions
 ## complete in a single tick; the done-check in JobRunner._tick_interact fires
@@ -54,9 +47,6 @@ func find_best_for(pawn) -> Job:
 		return j
 
 	# ── 2. Sow pass — only if no harvest work exists ─────────────────────────
-	# Pawn must not already be carrying something (no double-carry).
-	if pawn.carried_item != null:
-		return null
 	return _find_sow(pawn)
 
 
@@ -89,11 +79,10 @@ func _find_harvest(pawn) -> Job:
 	return j
 
 
-## Scan World.crops for the nearest sowable (TILLED) crop, find a reachable
-## grain item to use as seed, and build a 4-toil sow job.
-## Returns null when no sowable tile or no grain exists.
+## Scan World.crops for the nearest sowable (TILLED) crop and build a 2-toil
+## sow job.  No seed item is consumed — sow is a free designation (Rimworld-style).
+## Returns null when no sowable crop is reachable.
 func _find_sow(pawn) -> Job:
-	# Find the nearest sowable crop the pawn can reach.
 	var best_crop = null
 	var best_crop_dist: int = 999999
 
@@ -114,45 +103,9 @@ func _find_sow(pawn) -> Job:
 	if best_crop == null:
 		return null
 
-	# Find the nearest free grain item in the world.
-	var best_grain = null
-	var best_grain_dist: int = 999999
-
-	for it in World.items:
-		if it.item_type != Item.TYPE_GRAIN:
-			continue
-		if it.being_carried:
-			continue
-		# Reachability pre-check for the grain item too.
-		if pawn.tile != it.tile and World.pathfinder != null:
-			if World.pathfinder.find_path(pawn.tile, it.tile).is_empty():
-				continue
-		var d: int = abs(it.tile.x - pawn.tile.x) + abs(it.tile.y - pawn.tile.y)
-		if d < best_grain_dist:
-			best_grain_dist = d
-			best_grain = it
-
-	if best_grain == null:
-		return null
-
 	var j := Job.new()
 	j.label = "Sow %s at %s" % [best_crop.crop_kind, best_crop.tile]
 	j.target_node = best_crop
-	# Walk to the grain, pick it up, walk to the crop tile, sow.
-	# on_sow_tick() transitions the crop TILLED → SOWN; after the interact toil
-	# the pawn still carries the consumed grain.  A trailing DROP toil deposits
-	# it at the pawn's current tile (which is the crop tile); the item simply
-	# falls on the ground and HaulingProvider re-hauls it.  This is intentional
-	# MVP behaviour — the player sees the seed "planted" and any excess grain is
-	# returned to the floor for hauling. A future refinement can consume it
-	# outright by adding a CONSUME toil kind to JobRunner.
-	j.toils.append(Toil.walk_to(best_grain.tile))
-	j.toils.append(Toil.pickup())
 	j.toils.append(Toil.walk_to(best_crop.tile))
 	j.toils.append(Toil.interact(best_crop.get_path(), &"on_sow_tick"))
-	# Deposit the consumed grain at the crop tile so HaulingProvider can route
-	# it back to a stockpile.  MVP simplification: the seed is not destroyed on
-	# sow — it becomes a floor item.  A future CONSUME toil kind in JobRunner
-	# would burn the item in-place without spawning a floor stack.
-	j.toils.append(Toil.deposit())
 	return j