Add file filtering with glob patterns to bake_folder

[schovi]

Problem

The bake_folder macro previously embedded all files from a directory into the binary with limited control. Users couldn't selectively include or exclude files based on patterns, forcing them to either:

• Bake entire directories (including unwanted test files, build artifacts, logs)
• Manually structure directories to separate desired files
• Use multiple bake_folder calls with complex directory layouts

This made it difficult to embed only production assets while excluding development/test files from the compiled binary.

Solution

Add glob pattern filtering to bake_folder via include_patterns and exclude_patterns parameters. Patterns support standard glob syntax (*, **, ?) and are applied at compile time to control which files get embedded.

The implementation adds pattern matching logic to the loader process that filters discovered files before embedding them. Include patterns act as whitelist (OR logic), exclude patterns as blacklist (OR logic), applied in that order.

Changes

Macro Interface (src/baked_file_system.cr:178):

• Add include_patterns and exclude_patterns parameters to bake_folder macro
• Serialize filter patterns as JSON for loader process communication
• Maintain backward compatibility (nil patterns = no filtering)

Pattern Matching Engine (src/loader/loader.cr:14):

• glob_to_regex(): Convert glob patterns to regex (* → [^/]*, ** → recursive paths, ? → single char)
• matches_pattern?(): Test if file path matches a glob pattern
• filter_files(): Apply include/exclude filters to file list

Loader Integration (src/loader/loader.cr:83):

• Accept filter patterns from macro via command-line arguments
• Apply filtering after directory scanning but before embedding
• Convert absolute paths to relative for pattern matching
• Preserve existing file discovery behavior when no filters specified

Documentation (README.md:40):

• Pattern syntax reference and examples
• Include/exclude usage patterns
• Combined filtering examples
• Use cases and important notes

Tests:

• Pattern matching unit tests (loader_spec.cr)
• End-to-end filtering integration tests (baked_file_system_spec.cr)
• Test fixtures for various directory structures (spec/storage/filters/)

Quality & Impact

✅ All tests passing (unit and integration)

Testing Coverage:

• Pattern matching correctness (wildcards, recursive paths)
• Include-only filtering (whitelist)
• Exclude-only filtering (blacklist)
• Combined filtering (include + exclude)
• Edge cases (empty results, no filters, dotfiles interaction)

Backward Compatibility: Fully preserved - existing code continues to work without changes.

Performance: Minimal impact - filtering runs once at compile time, zero runtime overhead.