docs: add Phase 5-1 through 6-3 specs, plans, and Cargo.lock

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

Cargo.lock

@@ -180,6 +180,13 @@ version = "1.1.2"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "1505bd5d3d116872e7271a6d4e16d81d0c8570876c8de68093a09ac269d8aac0"
 
+[[package]]
+name = "audio_demo"
+version = "0.1.0"
+dependencies = [
+ "voltex_audio",
+]
+
 [[package]]
 name = "autocfg"
 version = "1.5.0"
@@ -2026,6 +2033,13 @@ checksum = "0b928f33d975fc6ad9f86c8f283853ad26bdd5b10b7f1542aa2fa15e2289105a"
 name = "voltex_asset"
 version = "0.1.0"
 
+[[package]]
+name = "voltex_audio"
+version = "0.1.0"
+dependencies = [
+ "voltex_math",
+]
+
 [[package]]
 name = "voltex_ecs"
 version = "0.1.0"
@@ -2037,6 +2051,14 @@ dependencies = [
 name = "voltex_math"
 version = "0.1.0"
 
+[[package]]
+name = "voltex_physics"
+version = "0.1.0"
+dependencies = [
+ "voltex_ecs",
+ "voltex_math",
+]
+
 [[package]]
 name = "voltex_platform"
 version = "0.1.0"