fix inconsistent error code

[varmar05]

For existing version we must return ProjectVersionExists not an generic upload error.
Stale upload and processed tmp files should be removed as well.

[coveralls]

Coverage Report for CI Build 36542401963

Coverage increased (+0.02%) to 92.667%

Details

• Coverage increased (+0.02%) from the base build.
• Patch coverage: 8 of 8 lines across 2 files are fully covered (100%).
• 1 coverage regression across 1 file.

Uncovered Changes

No uncovered changes found.

Coverage Regressions

1 previously-covered line in 1 file lost coverage.

File	Lines Losing Coverage	Coverage
server/mergin/sync/public_api_v2_controller.py	1	89.35%

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Coverage Stats

Relevant Lines:	11155
Covered Lines:	10337
Line Coverage:	92.67%
Coverage Strength:	0.93 hits per line

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💛 - Coveralls