Upload API — Publish and Update project files

[MariusStorhaug]

Parent: #4

Delivers functions for uploading new files to CurseForge projects and updating existing file metadata. These are the primary write operations for mod authors managing their releases.

Acceptance criteria:

• Publish-CurseForgeProjectFile uploads a file with metadata (multipart/form-data)
• All upload metadata fields supported: Changelog, ChangelogType, DisplayName, GameVersions, ReleaseType, Relations, ParentFileId
• Update-CurseForgeProjectFile updates metadata on an existing file
• Both functions return the file ID on success
• SupportsShouldProcess enabled (state-mutating operations)
• Unit tests cover metadata serialization and multipart form construction

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Endpoints:

Function	Method	Path	Content-Type
Publish-CurseForgeProjectFile	POST	/api/projects/{projectId}/upload-file	multipart/form-data
Update-CurseForgeProjectFile	POST	/api/projects/{projectId}/update-file	multipart/form-data

Upload metadata fields:

{
    "changelog": "string",
    "changelogType": "text|html|markdown",
    "displayName": "string",
    "parentFileID": 42,
    "gameVersions": [157, 158],
    "releaseType": "alpha|beta|release",
    "relations": {
        "projects": [{
            "slug": "string",
            "type": "embeddedLibrary|incompatible|optionalDependency|requiredDependency|tool"
        }]
    }
}

Update metadata fields: Same as upload minus the file, plus mandatory fileID.

Decision: Publish- verb for new uploads (creating a release), Update- verb for modifying existing (matches PowerShell verb semantics). Both use SupportsShouldProcess since they mutate remote state.

Blocked by: #11 (needs Upload API client)

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Sub-issues

See linked Tasks below.