List files from local cache when pending S3 upload

[Leonorus]

Issue #7: Terraform bpg/proxmox provider fails to read back files immediately after upload — failed to read file from "s3-iso:snippets/cloud-config-ubuntu.yaml".

Root cause: When PVE writes a file directly to the cache directory (e.g. via the Terraform provider), the file watcher needs 3+ seconds (debounce + stability check) before uploading to S3 and indexing metadata. The /v1/list endpoint only queries S3, so the file is invisible until the watcher completes the upload. The provider tries to read the file back immediately and fails because list_volumes() doesn't include it.

Fix: Modify handleList in internal/api/api.go to scan the local cache directory after querying S3, merging any files that exist locally but aren't yet in S3 into the response. Also improved the S3-unreachable fallback path to return locally cached files instead of an empty list.

[davekempe]

Looks good overall — clean approach, solid test coverage. One minor suggestion:

mergeLocalFiles should skip the .meta directory when recursing for images content. Currently it would treat .meta/ as a vmid subdirectory if it existed inside a content dir. Low risk since .meta lives at the cache root, but worth guarding:

if content == "images" {
    if entry.Name() == ".meta" {
        continue
    }
    // Recurse into VM ID subdirectories for images

[Leonorus]

mergeLocalFiles now skips the .meta directory when recursing into subdirectories for images content

[davekempe]

Looks good — .meta guard added, tests pass, clean approach.