Preserve Confluence Server REST URL compatibility

[hkwi]

Summary

The ConfluenceServer class in 5.0.0 changed the client to append the configured API root and version to its base URL. Existing calls that already pass paths such as rest/api/content/... therefore construct URLs such as /rest/api/1.0/rest/api/content/....

This breaks the established Confluence Server REST API URL used by on-premises installations. It also incorrectly places non-REST browser endpoints, such as PDF and Word exports, below the REST API root.

Changes

• Keep the Confluence site/context URL as the ConfluenceServer base URL, matching 4.x behavior.
• Prefix only unrooted Server REST resources at request time.
• Leave legacy rest/api/... paths, experimental REST paths, attachment download links, and browser/UI paths unchanged.
• Apply explicitly configured api_root and api_version values to unrooted REST resources without duplicating rooted paths.
• Preserve the existing method-level path expectations instead of rewriting them to fit the new URL layout.
• Add final HTTP URL regression coverage for relative REST resources, 4.x-style post/put/delete paths, explicit API versions, and PDF/Word export paths.

This keeps the Cloud/Server class split introduced in 5.x while restoring compatibility for existing Confluence Server clients.

Testing

• Focused Confluence tests: 168 passed, 6 skipped.
• Full test suite: 1027 passed, 10 skipped.
• Black check: passed for both changed files.

[gonchik]

@hkwi thanks

[codecov]

Codecov Report

❌ Patch coverage is 85.00000% with 3 lines in your changes missing coverage. Please review.
✅ Project coverage is 59.92%. Comparing base (996ea93) to head (cd2108c).
⚠️ Report is 1 commits behind head on master.

Files with missing lines	Patch %	Lines
atlassian/confluence/server/__init__.py	85.00%	1 Missing and 2 partials ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #1654      +/-   ##
==========================================
+ Coverage   59.82%   59.92%   +0.09%     
==========================================
  Files         104      104              
  Lines       17316    17334      +18     
  Branches     1797     1801       +4     
==========================================
+ Hits        10360    10387      +27     
+ Misses       6524     6519       -5     
+ Partials      432      428       -4     

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