Add Phase 2 implementation: pairs/dance elements, ISU validation, docs

- Add anv-semantics crate with ISU rules validation engine
  - Discipline-specific rules (singles, pairs, ice dance)
  - Element count validation per segment type
  - Constraint checking (no pairs elements in singles, etc.)

- Extend parser for pairs and ice dance elements:
  - Lifts (Gr1-Gr5) with levels
  - Throws with rotation counts
  - Twists with rotation and level
  - Death spirals with edge and level
  - Choreographic elements (spiral, spread, ina, hydroblading, pivot)

- Add rhythm and exhibition segment types

- Update README.adoc with:
  - Architecture diagram
  - Complete syntax documentation
  - CLI command reference
  - Examples for all disciplines
  - Current implementation status

- Update ROADMAP.adoc with:
  - Visual progress indicator
  - Detailed task completion tracking
  - Test coverage summary (90+ tests)
  - Technical debt section

Author: claude

Cargo.lock

@@ -7,6 +7,7 @@ members = [
     "crates/anv-core",
     "crates/anv-syntax",
     "crates/anv-types",
+    "crates/anv-semantics",
     "crates/anv-cli",
 ]
 
@@ -25,6 +26,7 @@ categories = ["compilers", "development-tools"]
 anv-core = { path = "crates/anv-core" }
 anv-syntax = { path = "crates/anv-syntax" }
 anv-types = { path = "crates/anv-types" }
+anv-semantics = { path = "crates/anv-semantics" }
 
 # Parsing
 logos = "0.14"