[dreddnafious]

Fixes #221.

Enable automatic src search-path detection for projects without explicit search-path configuration. An unconfigured layout such as this must connect imports to their definitions:

demo/
├── pyproject.toml       # project name/version
├── src/demo/__init__.py
├── src/demo/core.py     # def handler(): ...
└── tests/test_core.py   # from demo.core import handler

Without the fallback, definitions can use src.demo.core while imports fail to resolve demo.core. With it, definitions and the two imported/runtime references share demo.core/handler()..

Configuration behavior

Apply autodetection after configuration initialization, only when both default extra paths and execution environments are absent. Preserve explicit extraPaths, including [], and execution-environment search order. Even a root-only execution environment conservatively suppresses this fallback. A src directory containing __init__.py remains a package rather than an automatic search root.

The original report compared newer upstream Pyright 1.1.411 with scip-python. This change uses the vendored API and deliberately does not copy newer CLI behavior unconditionally: prepending src can otherwise shadow explicitly configured environment paths.

Verification

• Added real-indexing cases for absent/empty configuration, explicit custom paths, competing execution-environment paths, explicit empty paths, and src/__init__.py.
• Assert imported/runtime references resolve to the expected definitions, not merely that indexing succeeds.
• Regenerated the two existing snapshots whose module identities intentionally lose the src. prefix.
• Production/development builds, all 21 snapshots, all 7 SCIP Jest tests, and formatting passed locally on Linux with Node 24.4.1 and Python 3.10.22. Native Windows/macOS execution was not performed locally.