[elementalvoid]

Closes #95.

Summary

The client now holds Immich's supported extensions in one list, so a file the
server cannot accept is never a sync item — no state row, no attempt, no
failure.

 scan / watcher (shared skip rule)
   hidden, symlink, temporary, system        skip (as before)
   XMP sidecar                                skip; it rides with its asset
+  extension not in Immich's allowlist        skip; count it for the folder
   everything else                            queue an item
+
+allowlist (crates/sync-core/src/skip.rs)
+  SUPPORTED_MEDIA_EXTENSIONS = 40 image + video extensions, one line to add

 folder row (V14 migration)
   last_scan_ns, last_upload_ns
+  unsupported                  # files the last scan refused

• Never queued: matching is case-insensitive on the extension; a file with
  no extension, .wma, .mp3, .flac are refused. The sidecar, temporary and
  system rules still win, so an .xmp of a skipped file is skipped with it.
• Count in the folder detail: Files Immich cannot accept: 3, only when it
  is above zero. Nothing on the dashboard, and the pending/uploaded/failed
  counts do not move. The count lives on the folder row, so it survives a
  restart and the signed-out view (operator decision).
• Log: one line per scan per folder with the count and the extensions seen
  (info when above zero, debug when zero), per-file detail at debug.
• Old rows: a row recorded before this rule, for a file the list now
  refuses and holding no server asset, is deleted by the next scan that sees
  the file; the startup requeue no longer sends such a path. A row that holds
  an asset keeps its mapping and version chain (R4).
• Server stays the authority: a file the list accepts and Immich still
  refuses remains the permanent unsupported_format failure with its readable
  reason.

Files: sync-core/src/{skip,scan,engine,store,status}.rs,
app/src/{status,engine,folder_panel}.rs, SPEC.md R2.2, GLOSSARY.md.

Evidence

• Before: a .wma in a source folder was queued, answered 415, and landed
  in Failed as a dead letter (issue Supported file formats #95).
  After: sync-core::it engine::a_format_immich_cannot_accept_is_never_an_item_or_a_failure
  — one refused .wma and one accepted .jpg: the .wma has no row, no
  attempt, no failed item, one upload request in total, and the folder detail
  count is 1.
• Count persistence: a_later_scan_clears_the_count_once_the_refused_file_is_gone,
  store::the_unsupported_count_arrives_on_a_v13_database.
• Old rows: a_scan_drops_rows_without_an_asset_for_a_format_the_allowlist_refuses
  (dropped with its attempt log; a row holding an asset kept).
• Server-side 415: a_415_is_one_permanent_failure_and_is_never_retried now
  pins the readable reason.
• UI: folder_detail::the_detail_names_the_files_immich_cannot_accept and the
  480 px window test assert the label; DashboardModel::from_engine keeps the
  global card at zero.
• Gate on the rebased tree: cargo fmt --all -- --check,
  cargo clippy --workspace --all-targets -D warnings,
  cargo nextest run --workspace — 951 passed, 2 skipped.
• Windows installer built from this branch (build-only release dispatch):
  https://github.com/elementalvoid/immich-sync/actions/runs/43374658579 —
  immich-sync_0.3.0_x64-setup.exe, sha256 a068f1ab…70ea7.

Merge Danger

Door: one-way for an install that has run this build — V14 adds
source_folder.unsupported (NOT NULL DEFAULT 0), and rolling the client back
after it opened a V14 database makes the older schema check refuse that
database. The migration itself is additive and safe to run forward.

Blast Radius: small — one new column, one count line in the folder detail,
and deletion of asset-less rows for formats the allowlist refuses.