Add support for `.ignore` files in file content attachment handler

The jp_attachment_file_content crate should respect .ignore files to make it easy to exclude certain patterns from being added by default, similar to how ripgrep and fd handle ignore files.

Context

Currently, the file content attachment handler only uses the patterns explicitly provided by the user. However, many projects use .ignore files (popularized by tools like ripgrep and fd) to specify files and directories that should be ignored by default across different tools.

According to the ripgrep documentation, .ignore files use the same gitignore syntax but are intended for tool-specific ignoring rather than version control ignoring. The ignore crate that we're already using supports loading .ignore files through the WalkBuilder API.

Proposed Implementation

Modify the get method in FileContent to use the ignore crate's built-in .ignore file support by configuring the WalkBuilder to respect .ignore files. This can be achieved by:

1. Enabling .ignore file support in the WalkBuilder configuration
2. Ensuring that .ignore files are loaded and processed before applying user-provided patterns
3. Maintaining the current behavior where explicit user patterns can override .ignore patterns

Resources

• https://github.com/dcdpr/jp/blob/main/crates/jp_attachment_file_content/src/lib.rs#L80-L121

Start in crates/jp_attachment_file_content/src/lib.rs, especially the FileContent get method around lines 80-121, and inspect how its ignore crate WalkBuilder is configured. The work is done when .ignore files are respected before user-provided patterns while explicit user patterns retain their current override behavior.