Support ignore patterns

[sobeaa]

code-slicer should support ignoring files by pattern.

Expected behavior:

• accept multiple ignore patterns
• exclude a file if any pattern matches
• apply ignores consistently during traversal and output generation
• keep current behavior unchanged when no ignore patterns are provided

Example:

code-slicer src/main.ts --ignore "**/*.test.ts" --ignore "src/generated/**"

Possible config shape:

type Options = {
  ignore?: readonly string[];
};

Acceptance criteria:

• multiple ignore patterns are supported
• matching files are not included in output
• matching directories are not traversed
• non-matching files are unaffected
• tests cover one pattern, multiple patterns, and overlapping patterns