refactor(server): NearbyInteractionBuffer from Resource to Component

Per-entity Component attached to PlayerCharacter instead of global
Resource. Makes the interaction buffer multiplayer-ready (D-009) —
each observer gets their own buffer without pipeline refactoring.

Updated all 8 files touching the buffer: system signatures, player
spawn bundles, and ~30 test spawn sites.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

server/tests/game_loop.rs

@@ -7,6 +7,7 @@ use settled_reach_server::bridge::tcp::TcpBridge;
 use settled_reach_server::bridge::types::*;
 use settled_reach_server::bridge::{BridgePlugin, BridgeResource};
 use settled_reach_server::knowledge::{KnowledgeGraph, KnowledgePlugin};
+use settled_reach_server::simulation::interaction::NearbyInteractionBuffer;
 use settled_reach_server::simulation::movement::{PlayerCharacter, TilePosition, WalkabilityMap};
 use settled_reach_server::simulation::SimulationPlugin;
 use std::io::{BufReader, BufWriter};
@@ -34,6 +35,7 @@ fn player_moves_north_through_full_pipeline() {
             PlayerCharacter,
             TilePosition::new(16, 16, 0),
             KnowledgeGraph::new(),
+            NearbyInteractionBuffer::default(),
         ));
 
         // Run one tick: receive input, process, validate movement, generate snapshot, send