Create Stigcode CLI

[rdwj]

Primary interface for all Stigcode operations.

Acceptance Criteria:

• stigcode import <sarif-file> — ingest SARIF and display summary
• stigcode export ckl — generate STIG Viewer checklist
• stigcode export report — generate ATO evidence report
• stigcode export coverage — generate control coverage matrix
• stigcode lookup --cwe <id> — query mapping database
• stigcode lookup --stig <V-id> — reverse lookup from STIG finding to CWEs
• stigcode stig import --xccdf <file> — ingest STIG source data
• stigcode version — show Stigcode version, mapping database version, supported STIG versions
• Support stdin piping: sanicode scan --format sarif ./app | stigcode export ckl -o checklist.ckl
• Exit code 0 = success, 1 = open findings in output, 2 = error
• --quiet mode for CI pipelines