Add CONTRIBUTING.md and SECURITY.md files

- Introduced a CONTRIBUTING.md file to guide contributors on setup, coding guidelines, and pull request processes.
- Added a SECURITY.md file outlining the security policy, reporting vulnerabilities, and responsible disclosure procedures.

SECURITY.md

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+## Security Policy
+
+### Supported Versions
+
+We aim to support the latest released version of `ollama4j` and the most recent minor version prior to it. Older versions may receive fixes on a best-effort basis.
+
+### Reporting a Vulnerability
+
+Please do not open public GitHub issues for security vulnerabilities.
+
+Instead, email the maintainer at:
+
+```
+koujalgi.amith@gmail.com
+```
+
+Include as much detail as possible:
+
+- A clear description of the issue and impact
+- Steps to reproduce or proof-of-concept
+- Affected version(s) and environment
+- Any suggested mitigations or patches
+
+You should receive an acknowledgement within 72 hours. We will work with you to validate the issue, determine severity, and prepare a fix.
+
+### Disclosure
+
+We follow a responsible disclosure process:
+
+1. Receive and validate report privately.
+2. Develop and test a fix.
+3. Coordinate a release that includes the fix.
+4. Publicly credit the reporter (if desired) in release notes.
+
+### GPG Signatures
+
+Releases may be signed as part of our CI pipeline. If verification fails or you have concerns about release integrity, please contact us via the email above.
+
+