Fix docs: align with actual implementation

- Rewrite euredocument-vs-value.eure: remove non-existent Value type,
  replace with FromEure/eure_json/NodeValue actual APIs
- Add "Design Proposal" banners to completion_architecture.eure and
  completion_with_error_recovery.eure (types not yet implemented)
- Mark schema-extensions.eure bundling section as not yet implemented
- Mark template-extensions.eure features as planned but unimplemented
- Fix cst-and-visitor.eure: CstInterpreter path, insert_node → create_node+add_child_by_segment
- Fix schemas.eure: $types[] → $types.name notation

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

Author: ryo33

docs/completion_architecture.eure

@@ -1,10 +1,16 @@
 $docs {
   title: Eure Completion System Architecture
-  description: This document describes a complete redesign of the Eure LSP completion system to use proper CST (Concrete Syntax Tree) traversal instead of string-based parsing.
+  description: Design proposal for the Eure LSP completion system using CST traversal instead of string-based parsing. The described types are not yet implemented.
 }
 
 "#": Eure Completion System Architecture
 
+"body" = ```markdown
+> **Design Proposal — Not Yet Implemented**
+>
+> This document describes a planned redesign of the Eure LSP completion system. The types and structs described here (`CompletionVisitor`, `CompletionContext`, `PositionMapper`, `CompletionPosition`) do not currently exist in the codebase. This document records the intended architecture for future implementation.
+```
+
 "toc".$toc = true
 
 @ "overview" {

docs/completion_with_error_recovery.eure

@@ -1,10 +1,16 @@
 $docs {
   title: Completion with Error Recovery Approach
-  description: We need to support completion for: - Trailing dots: @ script. (complete after dot) - Empty values: key = (complete value) - Partial keys: @ scr (complete key)
+  description: Design proposal for error-recovery-based completion. The described types (ErrorBasedCompletion, PathExtractorVisitor) are not yet implemented.
 }
 
 "#": Completion with Error Recovery Approach
 
+"body" = ```markdown
+> **Design Proposal — Not Yet Implemented**
+>
+> This document describes a planned approach for completion with error recovery. The types described here (`ErrorBasedCompletion`, `PathExtractorVisitor`, `ErrorContext`, `PathContext`) do not currently exist in the codebase. This document records the intended architecture for future implementation.
+```
+
 "toc".$toc = true
 
 @ "problem-statement" {

docs/cst-and-visitor.eure

@@ -265,7 +265,7 @@ The combination of auto-generated, type-safe node access (`Handle` and `View`) a
   "##": CstInterpreter: Extracting Values from CST
 
   "body" = ```markdown
-While the `CstVisitor` trait provides a generic way to traverse the CST, the `CstInterpreter` struct (in `value_visitor.rs`) provides a specialized implementation for extracting structured data from Eure documents.
+While the `CstVisitor` trait provides a generic way to traverse the CST, the `CstInterpreter` struct (in `crates/eure/src/document/interpreter.rs`) provides a specialized implementation for extracting structured data from Eure documents.
 ```
 
   @ "cstinterpreter-overview" {
@@ -337,7 +337,8 @@ schema_validator.validate(&document); // Can report exact error locations
 
     "rust-snippet" = ```rust
    // Internally, bindings like `user.name = "Alice"` become:
-   document.insert_node(vec![PathSegment::Ident("user"), PathSegment::Ident("name")], Value::String("Alice"))
+   let node_id = document.create_node(NodeValue::Primitive(PrimitiveValue::Text(Text::plain("Alice"))));
+   document.add_child_by_segment(user_id, PathSegment::Ident("name".into()), node_id)?;
 ```
 
     "body-2" = ```markdown