Update README with Postman import and export commands

[vedssharma]

Documents the new apicli export postman and apicli import postman
commands, adds them to the Features list, and lists the new cmd files
in the Project Structure section.

https://claude.ai/code/session_0115ziB5BgJGej4QDFPRDWdt

[claude]

PR Review: Update README with Postman import and export commands

This is a documentation-only PR that looks well-structured overall. A few observations:

Positives

• Clear feature bullet points added to the Features list
• Good use of code examples covering common use cases
• The folder-flattening behavior for nested Postman folders is explicitly documented — helpful for users migrating from Postman
• The append behavior for existing collections is noted
• Project structure section kept up to date

Minor Suggestions

Ambiguous export example:
The comments in this block could be clearer:
```bash

Write output to a file

apicli export postman --collection my-api --output my-api.postman.json
apicli export postman --output all-collections.postman.json
```
The second example (no --collection, no --history) implies it exports all collections, but the comment just says "Write output to a file." Consider splitting into two comments or adding a preceding example showing stdout for all collections explicitly, e.g.:
```bash

Export all collections to a file

apicli export postman --output all-collections.postman.json
```

Error handling / edge cases:
Worth briefly noting what happens in failure scenarios:

• What if the import file doesn't exist or is malformed?
• What if --collection references a non-existent collection during export?

Even a single line like "Returns a non-zero exit code with an error message on failure" would help users scripting with these commands.

v2.0 vs v2.1 import distinction:
The import section mentions supporting both v2.0 and v2.1 but doesn't describe any behavioral differences between them. If there are none, that's fine — but if there's any feature parity gap it's worth documenting.

Summary

No blocking issues. The docs are clear and usable as-is. The suggestions above are minor improvements to help power users and scripters.