feat: dependency graph section in llms-full.txt

[wuzzzzaah]

This PR adds a "Dependency Graph" section to the llms-full.txt output.

Key changes:

• src/llmstxt_gen/parsers/base.py: Added imports field to ParsedModule.
• 14 language parsers in src/llmstxt_gen/parsers/: Implemented logic to extract import/include/require/use statements and populate the imports list.
• src/llmstxt_gen/renderer.py: Implemented a path mapping resolution helper that matches import strings (dotted or sub-paths) against project modules. Added a section to render_full that displays these dependencies.
• tests/test_renderer.py: Added test_render_full_includes_dependency_graph to ensure proper functionality and filtering of third-party imports.

The dependency graph helps LLMs understand project structure by identifying entry points vs internals. Module paths are resolved even when imported via dotted names or sub-paths (e.g., models.user resolving to src/models/user.py).

Fixes #64

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PR created automatically by Jules for task 17053758233463198368 started by @wuzzzzaah

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