refactor(build): auto-discover subpackages with setuptools find

[CyanoTex]

Summary

Follow-up to #110 (and previously #97). Switches [tool.setuptools] from a hand-maintained explicit packages list to [tool.setuptools.packages.find], scanning the three packages/*/src roots. New subpackages now ship in the wheel automatically — no more drift.

What changed

pyproject.toml:

• Removed the 26-entry explicit [tool.setuptools] packages = [...] list.
• Added [tool.setuptools.packages.find] with where = ["packages/core/src", "packages/cli/src", "packages/server/src"], include = ["repowise*"], namespaces = true (top-level repowise is a PEP 420 namespace package across the three src roots).
• Existing [tool.setuptools.package-dir] mapping and [tool.setuptools.package-data] entries are unchanged.

Net diff: +5/-33 lines.

Verification

Built the wheel before and after the edit on the same origin/main (0.4.1) base and diffed the package list inside the wheel. Identical contents, both manifests have 26 packages, all 15 .scm query files and 12 .j2 template files are still bundled.

$ uv build --wheel
Successfully built dist/repowise-0.4.1-py3-none-any.whl

$ python -c "import zipfile; z = zipfile.ZipFile('dist/repowise-0.4.1-py3-none-any.whl'); \
    pkgs = sorted(set('/'.join(n.split('/')[:-1]) for n in z.namelist() if n.endswith('__init__.py'))); \
    print(len(pkgs), 'packages')"
26 packages

$ diff baseline_packages.txt after_packages.txt
(empty)

Spot-check on package-data:

.scm files: 15
.j2 files: 12
First 3 .scm: ['repowise/core/ingestion/queries/c.scm', 'repowise/core/ingestion/queries/cpp.scm', 'repowise/core/ingestion/queries/csharp.scm']
First 3 .j2: ['repowise/core/generation/templates/api_contract.j2', 'repowise/core/generation/templates/architecture_diagram.j2', 'repowise/core/generation/templates/claude_md.j2']

Open questions / risks

• namespaces = true is required because no repowise/__init__.py exists in any of the three src roots; the top-level repowise is a PEP 420 namespace package. Verified by find packages -path "*/repowise/__init__.py" returning nothing.
• The package-dir mapping is kept as-is — it's consistent with what find discovers and removing it would be an orthogonal cleanup.

Test plan

• uv build --wheel succeeds on the new config
• Built wheel package set is byte-for-byte identical to the 0.4.1 wheel built from origin/main
• .scm and .j2 package-data files still ship
• CI green