v0.4.65: swap kernel-mount NFS for userspace SMB (smbclient)

v0.4.64's NFS path didn't work on Unraid even with --privileged
because Unraid's base kernel ships without the nfs/nfsv4 client
modules — and no container-side configuration can load a host kernel
module. SMB has the same kernel-mount problem (`mount -t cifs` needs
the cifs module) but it also has a usable *userspace* client: Samba's
`smbclient` CLI, which speaks the SMB protocol over a plain TCP socket
with no kernel involvement. This is the same approach Bootimus uses,
and works in every container regardless of host kernel modules or
container capabilities.

What's gone:

* `crates/iso-store/src/nfs.rs` (in entirety)
* `NfsManager`, `NfsMount`, `NfsAddRequest`, `NfsVersion` types
* `IsoSource::Nfs` variant
* `IsoStore::nfs_root` / `IsoStore::set_nfs_root`
* `/api/nfs`, `/api/nfs/:id`, `/api/nfs/:id/scan` routes
* `nfs` terminal command
* Storage tab's NFS shares card and the v0.4.64 fstab-options
  diagnostics work (the whole error path is moot now)

What's new:

* `crates/iso-store/src/smb_share.rs` — `SmbShareManager` that drives
  `smbclient` as a subprocess. Indexes shares via `smbclient -c "ls
  *.iso"` and streams files via `smbclient -c "get file -"` piped
  straight into HTTP response bodies. No local cache, no double disk
  usage.
* `IsoSource::Smb { share_id, relative_path }` variant.
* `IsoStore::iso_path_for` returns None for SMB sources — the HTTP
  ISO download handler dispatches on the source kind and streams via
  the SmbShareManager when it's SMB.
* `/api/smb-shares` + `/api/smb-shares/:id` + `/api/smb-shares/:id/scan`
  routes.
* `share` terminal command (`list | add //srv/share [auth] | remove |
  scan`). Auth spec is `guest` or `user:password`.
* Storage tab: SMB shares card replaces the NFS one. Two-column form
  for server + share name, three-column form for guest checkbox /
  username / password. Username and password fields auto-disable when
  Guest is checked.
* Credentials live under <work_dir>/smb_creds/<id>.cred at 0600
  permissions so they don't leak through `ps`. Persisted state at
  <work_dir>/smb_shares.json (sans password — re-entered on add /
  re-scan).

Why subprocess and not a Rust crate:

* The Debian runtime image already ships the `samba` package
  (Dockerfile line 84) — `smbclient` is right there.
* Library options (pavao, etc.) wrap libsmbclient so they still pull
  in the same C library at runtime.
* Subprocess gives operators a verifiable mental model — anything
  OpenPXE can do over SMB, they can reproduce by running `smbclient`
  manually at a shell.

Range-request limitation, called out in the smb_share.rs module docs
and the UI explainer: `smbclient -c 'get file -'` is a sequential
whole-file stream. HTTP range requests on SMB-sourced ISOs return
416. PXE workloads (iPXE chain, casper sanboot, wimboot) do
whole-file sequential reads, so this works in practice. A follow-up
release can add libsmbclient-based seek if a real workload needs it.

Stderr-to-hint translation patterns mirror v0.4.64's NFS work:
NT_STATUS_LOGON_FAILURE → "check credentials", BAD_NETWORK_NAME →
"check share name", connection refused / timeout → "verify
reachability + firewall", etc. UI renders the raw smbclient error
plus the hint as two lines.

Tests (149 total, was 142 in v0.4.64):
* smb_share parser tests covering ISO + skipped directory, filenames
  with spaces, non-ISO filtering.
* hint_for() translation tests for the dominant NT_STATUS codes.
* Server normalization (smb://, cifs://, \\, // prefixes all stripped).
* HTTP integration: shares list starts empty, invalid server / missing
  username / path in share name all rejected with actionable hints.

`cargo clippy --workspace --all-targets -- -D warnings` clean.

Co-Authored-By: Claude Opus 4.7 (1M context) <[email protected]>

Cargo.toml

@@ -12,7 +12,7 @@ members = [
 ]
 
 [workspace.package]
-version = "0.4.64"
+version = "0.4.65"
 edition = "2021"
 rust-version = "1.95"
 license = "MIT OR Apache-2.0"