feat(simulation): add A* pathfinding and NPC path following

Implements tickets #237 and #238 for Sprint 3:
- Add pathfinding crate dependency for A* algorithm
- PathRequest component triggers compute_paths system which uses
  cardinal-neighbor A* with manhattan distance heuristic
- ComputedPath component with step navigation (next_step, advance,
  is_complete) and PathBlocked marker for no-route cases
- MovementSpeed component throttles NPC movement (ticks_per_step)
- follow_paths system advances NPCs along computed paths, creating
  MoveIntent per step; cleanup_path_blocked removes markers after
  one tick
- System ordering: input → compute_paths → follow_paths →
  validate_movement → cleanup_path_blocked → advance_tick

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

server/Cargo.lock

@@ -378,6 +378,18 @@ dependencies = [
  "windows-sys",
 ]
 
+[[package]]
+name = "deprecate-until"
+version = "0.1.1"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "7a3767f826efbbe5a5ae093920b58b43b01734202be697e1354914e862e8e704"
+dependencies = [
+ "proc-macro2",
+ "quote",
+ "semver",
+ "syn",
+]
+
 [[package]]
 name = "derive_more"
 version = "2.1.1"
@@ -595,6 +607,15 @@ dependencies = [
  "hashbrown",
 ]
 
+[[package]]
+name = "integer-sqrt"
+version = "0.1.5"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "276ec31bcb4a9ee45f58bec6f9ec700ae4cf4f4f8f2fa7e06cb406bd5ffdd770"
+dependencies = [
+ "num-traits",
+]
+
 [[package]]
 name = "js-sys"
 version = "0.3.85"
@@ -701,6 +722,20 @@ version = "2.2.1"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "f38d5652c16fde515bb1ecef450ab0f6a219d619a7274976324d5e377f7dceba"
 
+[[package]]
+name = "pathfinding"
+version = "4.14.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "59ac35caa284c08f3721fb33c2741b5f763decaf42d080c8a6a722154347017e"
+dependencies = [
+ "deprecate-until",
+ "indexmap",
+ "integer-sqrt",
+ "num-traits",
+ "rustc-hash",
+ "thiserror",
+]
+
 [[package]]
 name = "pin-project"
 version = "1.1.10"
@@ -846,6 +881,12 @@ dependencies = [
  "serde",
 ]
 
+[[package]]
+name = "rustc-hash"
+version = "2.1.1"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "357703d41365b4b27c590e3ed91eabb1b663f07c4c084095e60cbed4362dff0d"
+
 [[package]]
 name = "rustc_version"
 version = "0.4.1"
@@ -904,6 +945,7 @@ dependencies = [
  "bevy_app",
  "bevy_ecs",
  "bincode",
+ "pathfinding",
  "rand",
  "rand_chacha",
  "rmp-serde",