fix: fallback to LICENSE file when package.json has no license field

[clanzhang]

Some packages like require-like don't declare a license field in package.json but ship a LICENSE file.
Read common license file names and infer the SPDX identifier from well-known license texts.

Closes #145

🔗 Linked issue

#145

🧭 Context

Some older packages like require-like don't declare a license field in
their package.json (this was common before npm standardized the field).
Instead, they ship a LICENSE file with the actual license text.

Currently, normalizePkgLicense() only reads from package.json, so these
packages show up as having no license at all in the inspector.

📚 Description

When package.json has no license or licenses field, fall back to
scanning common license file names (LICENSE, LICENSE.md, LICENCE, etc.)
in the package directory and infer the SPDX identifier from well-known
license text patterns.

Changes:

• Added detectLicenseFromFile() in package-json.ts that reads license
  files and matches text patterns for MIT, ISC, Apache-2.0, BSD-2-Clause,
  BSD-3-Clause, and UPL-1.0
• Updated resolvePackage() in resolve.ts to call the fallback when
  normalizePkgLicense() returns undefined
• Added unit tests covering all supported license types and edge cases

Not changed:

• The registry-based resolver (registry/resolve.ts) is unaffected — it
  has no filesystem access
• normalizePkgLicense() itself is untouched; the fallback is only applied
  in the filesystem-based resolvePackage()

[pkg-pr-new]

Open in StackBlitz

npm i https://pkg.pr.new/node-modules-inspector@204

npm i https://pkg.pr.new/node-modules-tools@204

commit: 184b3f3