[codex] Expose core workflow API endpoints

[jkendall327]

Summary

Refs #209.

This adds a broader REST control-plane slice for the workflows that were still trapped behind Blazor viewmodels or direct service calls:

• media details by hash, including repository, tags, notes, and media URL
• notes list/create/update/delete endpoints
• tag read and autocomplete suggestion endpoints
• repository transition endpoint for inbox/archive/trash moves
• duplicate scan/list/resolve endpoints
• download queue/status/result/pause/resume/cancel/retry endpoints
• subscription list/create/delete endpoints instead of the previous NotImplementedException
• /files/query/count for API-side search result counts
• typed API DTOs for the newly exposed durable workflow routes
• OctansClient.ImportFilesAsync now matches the server contract by returning the accepted import job rather than the old synchronous ImportResult

Notes

This keeps the existing /files and /files/query routes compatible for now, so they still expose HashItem. A later pass can move those legacy routes onto stable file/result DTOs and add paging/structured query errors without breaking the current client surface in the same PR.

Validation

• dotnet test Octans.slnx -m:1