minor: add G701-G706 rule-to-CWE mappings and CWE-117, CWE-918 entries

[costela]

Extends the ruleToCWE map to include the taint analysis rules introduced in #1486.

• issue/issue.go: Added G701→CWE-89, G702→CWE-78, G703→CWE-22, G704→CWE-918, G705→CWE-79, G706→CWE-117
• cwe/data.go: Added missing CWE-117 (Log Injection) and CWE-918 (SSRF) weakness definitions
• issue/issue_test.go: Test coverage for all six new mappings

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 81.01%. Comparing base (befce8d) to head (c6a9666).
⚠️ Report is 3 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #1606      +/-   ##
==========================================
+ Coverage   80.62%   81.01%   +0.39%     
==========================================
  Files         107      108       +1     
  Lines       10234    10010     -224     
==========================================
- Hits         8251     8110     -141     
+ Misses       1468     1418      -50     
+ Partials      515      482      -33     

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