[Duplicate] Feature/artifact upload

[LinseCed]

Important

Duplicate of #110

Related issue

Closes #92
Closes #245
Closes #62

Short summary

Implements project-scoped artifact retrieval and integrates manual uploads into the unified artifact model.

Changes include:

• Added GET /api/v1/projects/{projectId}/artifacts/{artifactId}/content.
• Added project-access and artifact-ownership validation.
• Added dynamic content type handling for raw artifact content.
• Integrated manual uploads with ingestion runs and unified artifact persistence.
• Added AI indexing and deindexing support.
• Added upload and deletion failure tracking.
• Updated artifact, ingestion, upload, listener, mapper, and controller tests.

Checks

• I verified the code makes sense intuitively
• The PR changes affect only this issue, no unrelated/unwanted code changes to other modules/code segments
• CI runs (./gradlew clean build, Keycloak)
• New business logic is unit tested, including WebMvcTest for API controllers
• The new functionality is tested manually

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Note: this is a fresh branch (feature/artifact-upload-dev-backup) rather than a reuse of the original feature/artifact-upload head, since that branch had dev merged into it multiple times to resolve real conflicts (and would have pulled in unrelated dev history). This branch is a clean cherry-pick of just #110's own net diff on top of dev-backup.