feat: granular context controls (include, exclude, size limits)

[Tanq16]

This PR introduces granular file filtering mechanisms to the ai-context project, allowing users to better manage their AI token budgets by targeting specific files and omitting irrelevant, bulky artifacts.

Key changes:

1. Replaced the simple ignoreList flag with an explicit -i (--include), -e (--exclude), and -s (--max-size).
2. Configured file path matching correctly using filepath.Match via the refactored PathFilter component.
3. Updated logic in processDirectory and generateDirectoryTree to skip paths via shouldInclude() and size limit assessments.
4. Expanded README.md to reflect these features with illustrative real-world examples ("Bug Hunt", "Learn & Implement").

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PR created automatically by Jules for task 17708558237133574544 started by @Tanq16

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