docs: update architecture gate progress

BUILD_IN_PUBLIC_PLAN.md:
- Mark systems gate items deterministic clock and headless checksum
  as complete; remaining gate work stays flagged as in-progress
- Rename TaskZone references to ActivityMarkers for consistency

LEARNING_ROADMAP.md:
- Add architecture gate progress note: first deterministic slice
  (SimulationClock, seeded streams, headless checksum) is implemented
- Update recommended implementation order to reflect shifted priorities

PROJECT_CONTEXT.md:
- Note that farm and forest markers have been deleted from main.tscn
- Update activity marker description (4 remaining: guard/study/rest/food)
- Add SimulationClock.gd and deterministic_simulation_test.gd to repo map
- Update technical debt: randomness is now seeded but RNG state is not
  yet serialized; clock is explicit but orchestration still lives on scene tree
- Gate status updated with completed first-slice summary

RESOURCE_NODE_MIGRATION.md:
- Mark Phase 4b (player parity) complete
- Phase 6 renamed from 'remove zone model' to 'replace activity markers'
  with progress note: TaskZone container and FarmZone/ForestZone deleted
- Update divergences to note farm/forest scene nodes have been removed

docs/PROJECT_CONTEXT.md

@@ -180,8 +180,9 @@ The current prototype implements a very early version of observe, autonomous
 task choice, physical travel, work completion, resource change, and direct
 player assistance. NPC `gather_food` and `gather_wood` tasks now use finite
 world `ResourceNode` instances (berry bushes and trees) rather than abstract
-zone markers. The zone markers remain only for player interaction and
-non-resource tasks. The migration is documented in
+zone markers. The obsolete farm and forest markers have been removed. Separate
+temporary activity markers remain for eating, rest, study, and patrol. The
+migration is documented in
 [the ResourceNode plan](RESOURCE_NODE_MIGRATION.md).
 
 ## Current technology
@@ -214,7 +215,8 @@ plugin content, not game architecture.
   follow/focus behavior.
 - Pressing `E` near a berry bush or tree extracts its configured yield into the
   village through the same `ResourceNode` contract used by NPCs.
-- Guard, study, and food interactions still use their temporary task zones.
+- Guard, study, rest, and food interactions still use temporary activity
+  markers.
 - `Escape` releases captured mouse input.
 
 ### Village simulation
@@ -288,24 +290,20 @@ result only when the task duration completes.
 Starvation can reduce productivity and eventually kill an NPC. Dead visuals
 stop moving, change appearance, and no longer collide.
 
-### Current task zones
+### Current activity markers
 
-The main scene contains placeholder zones for:
+The main scene contains placeholder activity markers for guard duty, study,
+rest, and food. The former farm and forest zones and their decorative geometry
+have been deleted.
 
-- farm;
-- forest;
-- guard duty;
-- study;
-- rest;
-- food.
+**Migration status:** NPC `gather_food` and `gather_wood` target `ResourceNode`
+instances (berry bushes and trees), with no marker fallback. The remaining
+markers are direct transitional targets for non-resource NPC tasks:
 
-The farm, forest, guard, study, rest, and food locations are represented by
-primitive geometry and a few tree assets.
-
-**Migration status:** NPC `gather_food` and `gather_wood` no longer use the
-farm and forest zones. They target `ResourceNode` instances (berry bushes and
-trees) instead. The zone markers remain for:
-- Non-resource NPC tasks (patrol → guard_zone, study → study_zone, rest → rest_zone, eat → food_zone)
+- patrol → guard marker;
+- study → study marker;
+- rest → rest marker;
+- eat → food marker.
 
 The player also harvests food and wood directly from nearby `ResourceNode`
 instances. Extraction returns the actual amount removed, updates the village by
@@ -465,8 +463,10 @@ NpcVisual navigates through the active world
 ├── simulation/
 │   ├── SimNPC.gd
 │   ├── SimVillage.gd
+│   ├── SimulationClock.gd
 │   └── SimulationManager.gd
 ├── tests/
+│   ├── deterministic_simulation_test.gd
 │   ├── flat_map_baseline_test.gd
 │   ├── jajce_world_scaffold_test.gd
 │   └── resource_node_player_parity_test.gd
@@ -493,14 +493,17 @@ NpcVisual navigates through the active world
 
 These are expected prototype constraints, not necessarily isolated bugs:
 
-- Task names and task-to-zone mappings are duplicated strings.
-- Task zones remain for non-resource activities; NPC and player food/wood
-  gathering use `ResourceNode` instances.
+- Task names and task-to-activity-marker mappings are duplicated strings.
+- Temporary activity markers remain for eating, rest, study, and patrol; NPC
+  and player food/wood gathering use `ResourceNode` instances with no fallback.
 - Mutable simulation state is not serializable through a defined save schema.
-- Randomness is not seeded for deterministic replay.
-- Simulation time depends on `_process` and a scene-tree node.
-- Automated coverage currently contains one headless player-parity and
-  resource-contention scenario; broader simulation coverage is still missing.
+- Simulation randomness is seeded and split into controlled per-NPC streams,
+  but RNG state is not yet part of a serializable save record.
+- An explicit fixed-step clock converts frame delta into simulation ticks, but
+  orchestration still lives on the scene-tree `SimulationManager`.
+- Automated coverage includes deterministic same-seed checksum,
+  player-parity/resource-contention, flat-map, and Jajce scaffold scenarios;
+  broader gameplay coverage is still missing.
 - Resources are global floating-point counters rather than items in locations
   and inventories.
 - NPCs do not have homes, schedules, possessions, memories, relationships,
@@ -710,10 +713,14 @@ Food and wood migration and the deliberately minimal `JajceWorld` scaffold,
 greybox, navigation spike, and stable-ID placement proof are complete. Do not
 proceed directly from that proof into open-ended beauty production.
 
-The architecture gate is now the active milestone:
+The architecture gate is now the active milestone. Its first slice is complete:
+
+- explicit fixed-step simulation clock;
+- seeded per-NPC decision and wander random streams;
+- headless fixed-seed scenario with a final-state checksum.
+
+The remaining gate work is:
 
-- deterministic clock and controlled random source;
-- fixed-seed headless scenarios with final-state checksums;
 - versioned serializable NPC, village, and resource state;
 - data-defined action and profession IDs;
 - separated action selection, execution, target resolution, and visual travel;