feat: add extended language validators and fix tokenizer crash bugs

Expand nimcheck with validators and tokenizers for C, C++, C#, Go, Rust,
Ruby, CSS, SQL, Markdown, Dockerfile, Makefile, Kotlin, Lua, Swift,
TypeScript, and XML. Register all flavors in the validator factory and
improve auto-detection scoring for the new languages.

Fix infinite tokenizer loops that caused OOM kills: closeBracket now
advances position, finishTokenizeStep guards stalled tokenization, and
Jinja/JS tokenizers no longer double-advance on brackets.

Fix block-balance false positives in Lua (for/do) and Ruby (postfix
unless), SQL trailing-comma detection across whitespace, and Makefile
tab literals in test fixtures.

tests/fixtures/markdown/edge_cases.md

@@ -0,0 +1,30 @@
+# Nimcheck
+
+---
+
+> A fast syntax validator.
+
+## Code Block
+
+```nim
+proc hello(): string =
+  result = "Hello"
+```
+
+```python
+def hello() -> str:
+    return "Hello"
+```
+
+| A | B | C |
+|---|---|---|
+| 1 | 2 | 3 |
+
+- [x] Done
+- [ ] Pending
+
+~~strikethrough~~
+
+Footnotes[^1]
+
+[^1]: A footnote.

tests/fixtures/markdown/invalid.md

@@ -0,0 +1,26 @@
+# Nimcheck
+
+> A fast syntax validator
+
+## Features
+
+- Fast
+- Accurate
+- 27+ languages
+
+## Unclosed Code Block
+
+```nim
+proc hello(): string =
+  result = "Hello"
+
+Still in code block without closing fence.
+
+## Broken Link
+
+[Broken](
+
+## Broken Table
+
+| A | B | C
+| 1 | 2 | 3 |

tests/fixtures/markdown/valid.md

@@ -0,0 +1,131 @@
+# Nimcheck: Universal Syntax Validator
+
+[![Nim](https://img.shields.io/badge/Nim-2.0+-yellow)](https://nim-lang.org)
+[![License](https://img.shields.io/badge/license-MIT-blue)](LICENSE)
+
+> **Fast, accurate syntax validation for 27+ languages.**  
+> Built in Nim. Zero dependencies beyond the standard library.
+
+---
+
+## Table of Contents
+
+1. [Features](#features)
+2. [Installation](#installation)
+3. [Quick Start](#quick-start)
+4. [Usage](#usage)
+5. [Supported Languages](#supported-languages)
+
+---
+
+## Features
+
+- **Multi-language** — validates Nim, Python, JavaScript, TypeScript, PHP, Ruby, Rust, Go, Lua, C, C++, C#, Java, Swift, Kotlin, Bash, HTML, XML, Jinja, JSON, YAML, TOML, CSS, SQL, Markdown, Dockerfile, Makefile
+- **Blazing fast** — compiles to native code via Nim
+- **Auto-detection** — identifies language from extension, shebang, or content analysis
+- **CI-friendly** — exit codes and structured output
+
+### Detection Methods
+
+| Priority | Method       | Confidence |
+|----------|-------------|------------|
+| 1        | Explicit    | 100%       |
+| 2        | Extension   | 90%        |
+| 3        | Shebang     | 95%        |
+| 4        | Content     | 70-95%     |
+
+---
+
+## Installation
+
+### From Source
+
+```bash
+git clone https://github.com/retoor/nimcheck
+cd nimcheck
+make release
+```
+
+### Via Nimble
+
+```bash
+nimble install nimcheck
+```
+
+---
+
+## Quick Start
+
+```bash
+nimcheck src/           # validate all files in src/
+nimcheck --flavor nim   # validate as Nim
+nimcheck --json         # JSON output
+nimcheck --watch        # watch mode
+```
+
+---
+
+## Usage Examples
+
+### Validate a single file
+
+```bash
+nimcheck src/main.nim
+```
+
+### Validate with explicit language
+
+```bash
+nimcheck --flavor python script.py
+```
+
+### Recursive directory scan
+
+```bash
+nimcheck --recursive project/
+```
+
+### JSON output for CI
+
+```bash
+nimcheck --json --recursive src/ > report.json
+```
+
+---
+
+## Supported Languages
+
+| Language    | Extensions                          |
+|-------------|-------------------------------------|
+| Nim         | `.nim`, `.nims`, `.nimble`          |
+| Python      | `.py`, `.pyw`, `.pyx`, `.pxd`       |
+| JavaScript  | `.js`, `.mjs`, `.cjs`               |
+| TypeScript  | `.ts`, `.tsx`                       |
+| PHP         | `.php`, `.phtml`                    |
+| HTML        | `.html`, `.htm`, `.xhtml`           |
+| XML         | `.xml`, `.svg`                      |
+| JSON        | `.json`, `.jsonc`                   |
+| YAML        | `.yaml`, `.yml`                     |
+| TOML        | `.toml`                             |
+| CSS         | `.css`                              |
+| SQL         | `.sql`                              |
+| Markdown    | `.md`, `.markdown`                  |
+| Ruby        | `.rb`                               |
+| Rust        | `.rs`                               |
+| Go          | `.go`                               |
+| Lua         | `.lua`                              |
+| C           | `.c`, `.h`                          |
+| C++         | `.cpp`, `.cxx`, `.hpp`              |
+| C#          | `.cs`                               |
+| Java        | `.java`                             |
+| Swift       | `.swift`                            |
+| Kotlin      | `.kt`, `.kts`                       |
+| Bash        | `.sh`, `.bash`                      |
+| Dockerfile  | `Dockerfile`                        |
+| Makefile    | `Makefile`                          |
+
+---
+
+## License
+
+MIT © [Retoor](https://github.com/retoor)