feat(pypi): add username-based package discovery

[paladini]

Problem

The PyPI generator previously only accepted explicit comma-separated package names:

```yaml
pypi: requests,flask,django
```

Unlike npm, RubyGems and Docker Hub — which all accept a username and auto-discover your packages — PyPI required users to know and list every package name upfront. This was inconsistent and inconvenient.

Solution

When a single value (no commas) is passed to `pypi:`, the generator now first attempts a username lookup via the PyPI XMLRPC `user_packages` API. If the user owns packages, those are fetched automatically. If no user is found, it falls back to treating the value as a single package name (backwards-compatible).

```yaml

New: by username — auto-discovers all your packages

pypi: your-username

Existing: explicit package names (unchanged)

pypi: package1,package2
```

Changes

• `src/generators/npm.ts`

  • Add `fetchPyPIUserPackages(username)` using the PyPI XMLRPC `user_packages` method
  • Update `pypiGenerator.generate()` to try username lookup when a single value is given, falling back to package-name mode
  • Populate `identity.contact.social` with the user's PyPI profile URL when resolved by username (mirrors npm/dockerhub behaviour)
  • Update `flagArg` and `description` to reflect both modes

• `templates/.mcp-me.yaml`

  • Document both usage modes with inline comments

Verified working (smoke tests)

DockerHub — already implemented, confirmed end-to-end:
```
[DockerHub] Fetching repos for paladini...
[DockerHub] Found 3 repositories.
Projects found: 3
```

PyPI by username — new feature, confirmed end-to-end:
```
[PyPI] Looking up packages for user "paladini"...
[PyPI] Found 2 package(s) owned by "paladini".
[PyPI] ✔ faker-job-brazil v0.0.1.dev0
[PyPI] ✔ pySpark-connector-kairosdb v0.1.0
Projects found: 2
```

PyPI by package names — existing behaviour, unchanged:
```yaml
pypi: requests,flask # still works as before
```

Test plan

• `pypi: paladini` → discovers 2 packages via username lookup, fetches metadata
• `dockerhub: paladini` → discovers 3 container images, fetches metadata
• `pypi: requests,flask` → fetches those packages explicitly (existing behaviour)
• `pypi: nonexistent-user-xyz` → falls back to treating value as a package name, logs "not found"
• TypeScript build passes (`npm run build`)

🤖 Generated with Claude Code