Split monolithic Python packages into per-subpackage components

[ethenotethan]

Summary

The Python discovery plugin previously emitted exactly one Component per pyproject.toml, even when the source tree contained many logically independent sub-packages. For monolithic Python codebases (the common case — PEP 621 has no workspace manifest like Cargo/npm), this hid the internal dependency structure that Flashlight's multi-agent analysis is designed to exploit.

This PR mirrors the Go plugin's single-module-monorepo approach: when a project has a flat- or src-layout source tree with ≥2 substantial top-level sub-packages, emit a Component per sub-package in addition to the root, with internal_dependencies derived from AST-based import analysis (handles both absolute from pkg.sub import X and relative from ..sub import X forms).

Classification per sub-package uses import-statement regex with word boundaries to avoid false positives (e.g., "dashboard" in a docstring was previously matching the "dash" frontend framework marker).

Changes

• agent/discovery/languages/python.py — add _find_source_package, _discover_subpackages, _scan_python_imports (with relative-import resolution), and _classify_subpackage; tighten classifier to use word-boundary matching on import statements.
• tests/discovery/test_python_plugin.py — 17 new tests covering flat/src layouts, relative imports, hyphenated project names, skip rules for tests/private dirs, min-sub-package threshold, classification, and the docstring-false-positive regression.

Validation

Validated end-to-end against jundot/omlx via GLM-5.1 on OpenRouter: 12 components discovered across 6 dependency-depth levels, correctly classifying the FastAPI-based api as SERVICE and everything else as LIBRARY.

Test plan

• pytest tests/discovery/test_python_plugin.py — 17 new tests plus existing coverage.
• End-to-end discovery run against a real monorepo confirms per-subpackage components and correct internal_dependencies edges.