fix: parse python relative import shorthand

[atharvasingh7007]

Summary

• parse Python shorthand relative imports like from . import models and from .. import utils as ".models" and "..utils"
• add parser coverage for shorthand relative imports
• add graph coverage showing those parsed imports resolve to internal module edges

Root cause

import_from_statement only recorded the module_name field. For shorthand relative imports, tree-sitter exposes that field as just . or .., so Stacklit dropped the imported module name and stored bare relative markers in info.Imports. That meant stacklit.json and DEPENDENCIES.md missed valid internal edges for common Python package layouts.

Impact

Python projects that use from . import module or from .. import package now produce correct dependency edges without any CLI or schema changes.

Validation

• go test ./...
• go build -o stacklit.exe ./cmd/stacklit
• manual sanity run on a temporary Python package using from . import models and from .. import shared

[thegdsks]

Looks good, nice catch on the shorthand form. Thanks for the contribution.