refactor(filesystem): split into 5 atomic free-function ops + use cases

Replaces the monolithic FileManager class + scattered helpers in
alfred/infrastructure/filesystem with five free functions, each
single-responsibility and pathlib-native:

  list_dir / create_dir / link_file / move_file / move_dir

The infra layer now raises typed exceptions (FilesystemError base
+ SourceNotFound / DestinationExists / NotADirectory / NotAFile /
PermissionDenied / CrossDevice / FilesystemOSError) instead of
returning {status: ok|error} dicts. No more get_memory() reads
from infra.

Application layer mirrors the same split: five free use cases
(<op>_use_case) wrap each infra op, guard inputs against escaping
the new DirectoryRoots VO (downloads / torrents / movies /
tv_shows), catch infra exceptions, and return frozen DTOs. Roots
are injected — no global state.

Legacy files kept on disk with _OLD suffix for reference during
the follow-up rewiring (FileManager, MediaOrganizer,
create_folder/move helpers; CreateSeedLinks/ListFolder/MoveMedia/
ManageSubtitles use cases, resolve_destination). They are no
longer exported from __init__, which intentionally breaks current
agent tool wrappers and downstream tests — re-wiring is the next
chunk of work on the unfuck branch.

CHANGELOG.md

@@ -15,6 +15,38 @@ callers).
 
 ## [Unreleased]
 
+### Changed
+
+- **`filesystem` infra + application rewritten as 5 atomic free
+  functions.** On branch `unfuck`. Replaces the monolithic
+  `FileManager` class + scattered helpers with five small, pure ops in
+  `alfred/infrastructure/filesystem/`: `list_dir`, `create_dir`,
+  `link_file`, `move_file`, `move_dir`. Each takes `pathlib.Path`
+  arguments and raises typed exceptions from a dedicated hierarchy
+  (`FilesystemError` → `SourceNotFound` / `DestinationExists` /
+  `NotADirectory` / `NotAFile` / `PermissionDenied` / `CrossDevice` /
+  `FilesystemOSError`) — no more `{"status": "ok" | "error"}` dicts at
+  the infra boundary, no more `get_memory()` reads.
+- **`filesystem` application: 5 use cases as free functions.** A
+  matching `<op>_use_case(path, …, roots: DirectoryRoots)` wraps each
+  infra op, guards inputs against escaping a new `DirectoryRoots` VO
+  (downloads / torrents / movies / tv_shows), catches infra exceptions,
+  and returns a frozen `<Op>Response` DTO. Roots are now injected, not
+  pulled from the global memory singleton.
+
+### Removed
+
+- `FileManager` / `MediaOrganizer` / `create_folder` / `move` from the
+  public API of `alfred.infrastructure.filesystem`. Their files remain
+  on disk renamed with an `_OLD` suffix (e.g. `file_manager_OLD.py`) so
+  the migration can finish on a follow-up commit without losing
+  reference material. They are no longer re-exported from `__init__`.
+- `CreateSeedLinksUseCase` / `ListFolderUseCase` / `MoveMediaUseCase` /
+  `ManageSubtitlesUseCase` / `resolve_destination` from the public API
+  of `alfred.application.filesystem`. Same `_OLD` rename treatment.
+  This intentionally breaks current tool wrappers and tests downstream
+  — re-wiring is the next chunk of work on this branch.
+
 ### Added
 
 - **`.alfred` v2 — Phase 4: v2-shaped `rescan_show` + new