Add --replace-gmi-ext parameter for .gmi to .html link conversion

This commit adds a new boolean parameter to convert .gmi links to .html in the output:
- Adds a new parseGeminiLink parameter to replace .gmi with .html in links
- Updates the CLI tool to expose --replace-gmi-ext flag
- Adds tests for the new functionality
- Updates documentation

🤖 Generated with [Claude Code](https://claude.ai/code)
Co-Authored-By: Claude <noreply@anthropic.com>

README.md

@@ -12,4 +12,24 @@ Running:
 
 ```shell
 ./dist/gmi2html <gemtext.gmi >gemtext.html
-```
+```
+
+Options:
+
+- `--no-container`: Don't output container HTML
+- `--replace-gmi-ext`: Replace .gmi extension with .html in links
+
+Example:
+
+```shell
+# Convert Gemini text and replace all .gmi links with .html
+./dist/gmi2html --replace-gmi-ext <input.gmi >output.html
+
+# Convert only the content without wrapping it in the HTML container
+./dist/gmi2html --no-container <input.gmi >output-content.html
+```
+
+Help:
+```shell
+./dist/gmi2html --help
+```