feat(simulation): implement content loader Phase 2 (#408)

Extend content loader to read and instantiate real YAML content into
ECS entities. 2-phase spawn pipeline: Phase 1 creates entities with
core components (Want, Tolerance, Contentment, Personality, Tells,
Skills), Phase 2 resolves cross-references (Relationships, Secrets,
Information via KnowledgeGraph, DailyRoutine).

Loads enums, entity attributes, pools, templates, triangles, and NPC
profiles. Handles stub files gracefully. 7 integration tests against
real content files plus edge case tests for invalid data.

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

server/Cargo.lock

@@ -616,6 +616,12 @@ dependencies = [
  "num-traits",
 ]
 
+[[package]]
+name = "itoa"
+version = "1.0.17"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "92ecc6618181def0457392ccd0ee51198e065e016d1d527a7ac1b6dc7c1f09d2"
+
 [[package]]
 name = "js-sys"
 version = "0.3.85"
@@ -902,6 +908,12 @@ version = "1.0.22"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "b39cdef0fa800fc44525c84ccb54a029961a8215f9619753635a9c0d2538d46d"
 
+[[package]]
+name = "ryu"
+version = "1.0.23"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "9774ba4a74de5f7b1c1451ed6cd5285a32eddb5cccb8cc655a4e50009e06477f"
+
 [[package]]
 name = "semver"
 version = "1.0.27"
@@ -938,6 +950,19 @@ dependencies = [
  "syn",
 ]
 
+[[package]]
+name = "serde_yaml"
+version = "0.9.34+deprecated"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "6a8b1a1a2ebf674015cc02edccce75287f1a0130d394307b36743c2f5d504b47"
+dependencies = [
+ "indexmap",
+ "itoa",
+ "ryu",
+ "serde",
+ "unsafe-libyaml",
+]
+
 [[package]]
 name = "settled-reach-server"
 version = "0.1.0"
@@ -950,6 +975,7 @@ dependencies = [
  "rand_chacha",
  "rmp-serde",
  "serde",
+ "serde_yaml",
  "thiserror",
  "tracing",
  "tracing-subscriber",
@@ -1164,6 +1190,12 @@ version = "0.2.6"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "ebc1c04c71510c7f702b52b7c350734c9ff1295c464a03335b00bb84fc54f853"
 
+[[package]]
+name = "unsafe-libyaml"
+version = "0.2.11"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "673aac59facbab8a9007c7f6108d11f63b603f7cabff99fabf650fea5c32b861"
+
 [[package]]
 name = "uuid"
 version = "1.20.0"