Add mermaid diagram documentation for VimScript parsing flow

[Copilot]

Documents how VimScript content is parsed and transformed into an AST using Vinter's Lexer, Parser, and Linter classes.

Changes

• docs/ARCHITECTURE.md: New architecture documentation with 7 mermaid diagrams:

  • Overall parsing flow (Lexer → Parser → Linter pipeline)
  • Sequence diagram of component interactions
  • Token and AST node class diagrams
  • Step-by-step parsing example
  • Linter rule traversal flowchart
  • Class relationships

• README.md: Added Architecture section linking to the new docs

Diagram Overview

flowchart LR
    A[VimScript Content] --> B[Lexer]
    B -->|tokens| C[Parser]
    C -->|AST| D[Linter]
    D -->|issues| E[Output]

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The documentation covers token types, AST node structures, and how lint rules traverse the tree to detect issues.

Original prompt

create a mermaid diagram of how a vimscript content will be parsed and turned into an AST using the Vinter classes

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