docs: update documentation with RC implementation status

- C_BACKEND.md: Update memory management from "Leaks" to "Scope-based RC",
  update comparison tables with Koka/Rust/Zig/Go
- LANGUAGE_COMPARISON.md: Add status column to gap tables, add RC row
- OVERVIEW.md: Add C backend RC to completed features, update limitations
- REFERENCE_COUNTING.md: Add "Path to Koka/Rust Parity" section with:
  - What we have vs what Koka/Rust have
  - Remaining work for full memory safety (~230 lines)
  - Performance optimizations for Koka parity (~600 lines)
  - Cycle detection strategy

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

docs/LANGUAGE_COMPARISON.md

@@ -279,6 +279,7 @@ Based on 2025 research, languages succeed through:
 | Practical Focus | No | Yes | Yes | Yes | Yes | **Yes** |
 | Schema Evolution | No | No | No | No | No | **Planned** |
 | Behavioral Types | No | No | No | No | No | **Planned** |
+| Reference Counting | Perceus | N/A | N/A | GC | N/A | **Scope-based** |
 | JIT Compilation | No | No | N/A | N/A | No | **Yes** |
 
 ### Lux's Potential Differentiators
@@ -324,14 +325,15 @@ run app() with { Http = mockHttp, Database = inMemoryDb }
 
 ### Critical Gaps (Blocking Adoption)
 
-| Gap | Why It Matters | Priority |
-|-----|----------------|----------|
-| **Ecosystem/Packages** | "You rarely build from scratch" (Python's success) | P0 |
-| **Generics** | Can't write reusable `List<T>` functions | P0 |
-| **String Interpolation** | Basic usability | P1 |
-| **File/Network IO** | Can't build real applications | P1 |
-| **Elm-Quality Errors** | "Famous error messages" drive adoption | P1 |
-| **Full Compilation** | JIT exists but limited | P2 |
+| Gap | Why It Matters | Priority | Status |
+|-----|----------------|----------|--------|
+| **Ecosystem/Packages** | "You rarely build from scratch" (Python's success) | P0 | ❌ Missing |
+| **Generics** | Can't write reusable `List<T>` functions | P0 | ✅ Complete |
+| **String Interpolation** | Basic usability | P1 | ✅ Complete |
+| **File/Network IO** | Can't build real applications | P1 | ✅ Complete |
+| **Elm-Quality Errors** | "Famous error messages" drive adoption | P1 | ⏳ Partial |
+| **Full Compilation** | Native binaries | P2 | ✅ C Backend |
+| **Memory Management** | Long-running services need it | P1 | ✅ RC Working |
 
 ### Developer Experience Gaps
 
@@ -345,13 +347,13 @@ run app() with { Http = mockHttp, Database = inMemoryDb }
 
 ### Ecosystem Gaps
 
-| Gap | Why It Matters |
-|-----|----------------|
-| No package registry | Can't share/reuse code |
-| No HTTP library | Can't build web services |
-| No database drivers | Can't build real backends |
-| No JSON library | Can't build APIs |
-| No testing framework | Can't ensure quality |
+| Gap | Why It Matters | Status |
+|-----|----------------|--------|
+| No package registry | Can't share/reuse code | ❌ Missing |
+| No HTTP library | Can't build web services | ✅ Http effect |
+| No database drivers | Can't build real backends | ❌ Missing |
+| No JSON library | Can't build APIs | ✅ Json module |
+| No testing framework | Can't ensure quality | ✅ Test effect |
 
 ---