Classify `.env` dotfiles as config paths

Summary

CONFIG_EXTENSIONS in packages/core/src/repowise/core/support_paths.py explicitly lists ".env" as a config extension, but is_doc_or_config_path() matches on PurePosixPath(path).suffix only — and pathlib reports an empty suffix for dotfiles (PurePosixPath('.env').suffix == ''). As a result the file literally named .env (at any depth) is never recognised as config, while foo.env is.

The same suffix-only idiom is duplicated in the knowledge-graph node classifier (_classify_file_type in packages/core/src/repowise/core/analysis/knowledge_graph.py), which therefore labels .env a generic "file" instead of "config".

Steps to reproduce

PYTHONPATH=packages/core/src python3 -c 'from repowise.core.support_paths import is_doc_or_config_path as f, file_population; print(is_doc_or_config_path(".env"), is_doc_or_config_path("proj/.env"), is_doc_or_config_path("foo.env")); print(file_population(".env", is_test=False))'

Expected vs actual

• Expected: is_doc_or_config_path('.env') → True (it is the canonical file the ".env" entry names), is_doc_or_config_path('proj/.env') → True, and file_population('.env', is_test=False) → "doc".
• Actual: False, False, True (for foo.env), and file_population('.env', …) → "production" — so .env files are treated as production code by every surface that hides non-production (entry points, tours, module grouping).

Evidence

• packages/core/src/repowise/core/support_paths.py:75-80 — CONFIG_EXTENSIONS contains ".env".
• packages/core/src/repowise/core/support_paths.py:84-87 — is_doc_or_config_path checks only .suffix, which is '' for .env.
• packages/core/src/repowise/core/analysis/knowledge_graph.py:167-172 — _classify_file_type repeats the suffix-only check (ext in _CONFIG_EXTENSIONS), so .env falls through to "file".
• Observed output: [('.env', False), ('proj/.env', False), ('foo.env', True), ('README.md', True)] and file_population('.env') == 'production' vs file_population('foo.env') == 'doc'.
• Dedup: searched existing issues and PRs (open and closed) for is_doc_or_config_path, CONFIG_EXTENSIONS, .env config classification, dotfile suffix, file_population — no plausibly related report (the only dotfile hits are unrelated feature/semantic matches).

Start with CONFIG_EXTENSIONS and is_doc_or_config_path() in packages/core/src/repowise/core/support_paths.py, then inspect _classify_file_type in packages/core/src/repowise/core/analysis/knowledge_graph.py. Run the reproduction command from the issue and verify that .env and proj/.env are recognised as config, file_population returns "doc", and the knowledge graph classifies .env as "config".