feat(simulation): multi-threaded executor + EntityRng (#843 Part B)

Enable Bevy multi-threaded executor via bevy_tasks multi_threaded
feature. Systems within the same TickPhase that don't share mutable
resources now run in parallel automatically.

Add EntityRng component — per-entity ChaCha20Rng seeded from
world_seed + StableId via splitmix64 mixing. More deterministic than
shared SimRng (order-independent). Migrate all monologue systems
(4 of 13 SimRng consumers) to EntityRng, removing contention that
serialized them against conversation/dialogue systems.

Add rayon dependency (infrastructure only, no par_iter calls yet).

SimRng retained for world-level randomness: conversation pairing,
knowledge transfer, dialogue, ticker, storyteller.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

server/Cargo.lock

@@ -306,6 +306,7 @@ dependencies = [
  "async-task",
  "atomic-waker",
  "bevy_platform",
+ "concurrent-queue",
  "crossbeam-queue",
  "derive_more",
  "futures-lite",
@@ -485,6 +486,25 @@ dependencies = [
  "crossbeam-utils",
 ]
 
+[[package]]
+name = "crossbeam-deque"
+version = "0.8.6"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "9dd111b7b7f7d55b72c0a6ae361660ee5853c9af73f70c3c2ef6858b950e2e51"
+dependencies = [
+ "crossbeam-epoch",
+ "crossbeam-utils",
+]
+
+[[package]]
+name = "crossbeam-epoch"
+version = "0.9.18"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "5b82ac4a3c2ca9c3460964f020e1402edd5753411d7737aa39c3714ad1b5420e"
+dependencies = [
+ "crossbeam-utils",
+]
+
 [[package]]
 name = "crossbeam-queue"
 version = "0.3.12"
@@ -581,6 +601,12 @@ dependencies = [
  "serde",
 ]
 
+[[package]]
+name = "either"
+version = "1.15.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "48c757948c5ede0e46177b7add2e67155f70e33c07fea8284df6576da70b3719"
+
 [[package]]
 name = "equivalent"
 version = "1.0.2"
@@ -605,6 +631,7 @@ source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "e13b66accf52311f30a0db42147dadea9850cb48cd070028831ae5f5d4b856ab"
 dependencies = [
  "concurrent-queue",
+ "parking",
  "pin-project-lite",
 ]
 
@@ -1094,6 +1121,26 @@ dependencies = [
  "getrandom",
 ]
 
+[[package]]
+name = "rayon"
+version = "1.11.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "368f01d005bf8fd9b1206fb6fa653e6c4a81ceb1466406b81792d87c5677a58f"
+dependencies = [
+ "either",
+ "rayon-core",
+]
+
+[[package]]
+name = "rayon-core"
+version = "1.13.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "22e18b0f0062d30d4230b2e85ff77fdfe4326feb054b9783a3460d8435c8ab91"
+dependencies = [
+ "crossbeam-deque",
+ "crossbeam-utils",
+]
+
 [[package]]
 name = "regex-automata"
 version = "0.4.14"
@@ -1260,6 +1307,7 @@ version = "0.1.34"
 dependencies = [
  "bevy_app",
  "bevy_ecs",
+ "bevy_tasks",
  "bincode",
  "clap",
  "crossbeam-channel",
@@ -1267,6 +1315,7 @@ dependencies = [
  "pathfinding",
  "rand",
  "rand_chacha",
+ "rayon",
  "rmp-serde",
  "ron",
  "rusqlite",