feat: auto-detect and correct ZFS blocksize for TrueNAS SCALE/CORE (#241)

* feat: auto-detect and correct ZFS blocksize for TrueNAS SCALE/CORE (#241)

SCALE requires >= 16k volblocksize; CORE works with 8k. Without correction,
creating a disk on SCALE with blocksize=8k triggers a ZFS warning and wastes
space on SCALE's minimum-4k-block pool layout.

Three changes:
- freenas_get_recommended_blocksize: fixes freenas_api_connect → freenas_api_check
  so product_name is actually populated before the SCALE check (was always returning
  8192 before this fix)
- freenas_parse_blocksize: new helper to compare "8k"/"16k"/integer blocksize strings
- alloc_image (both 8.x and 8.4.x patches): always detect recommended blocksize for
  freenas provider; if configured < recommended, override for this call AND persist
  the correction back to storage.cfg via lock_storage_config
- on_add_hook (8.4.x patch only): detect at storage creation time and correct $scfg
  before write_config saves it — no extra write needed

Tested on pve01-hq (PVE 8.4.19) against Tank02 (SCALE 24.10.2.1):
- Disk created with blocksize=8k → task log shows correction message, storage.cfg
  updated to 16384, no volblocksize warning from TrueNAS
- Disk created with blocksize=16384 → no-op, clean TASK OK

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

* ci: add validate-patches step for ZFSPlugin PVE 8.4.x patch

ZFSPlugin-8.4.14_1.pm.patch has been in the build since v2.3.0 but was
never dry-run validated in CI. Now that we have the 8.4 orig committed
(ZFSPlugin-8.4.14_1.pm.orig from libpve-storage-perl 8.3.8), wire it up.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

* fix: replace explicit return undef with bare return (perlcritic)

Subroutines::ProhibitExplicitReturnUndef violation in
freenas_get_recommended_blocksize. Bare return in list context returns
an empty list rather than a list containing undef, which is the
correct Perl idiom.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

---------

Co-authored-by: Claude Sonnet 4.6 <noreply@anthropic.com>

.github/workflows/build.yml

@@ -69,6 +69,13 @@ jobs:
             < stable-8/perl5/PVE/Storage/ZFSPlugin.pm.patch \
             && echo "ZFSPlugin PVE-8 patch: OK"
 
+      - name: "Dry-run patch: ZFSPlugin (PVE 8.4.x)"
+        run: |
+          patch --dry-run --ignore-whitespace \
+            stable-8/perl5/PVE/Storage/ZFSPlugin-8.4.14_1.pm.orig \
+            < stable-8/perl5/PVE/Storage/ZFSPlugin-8.4.14_1.pm.patch \
+            && echo "ZFSPlugin PVE-8.4 patch: OK"
+
       - name: "Dry-run patch: apidoc.js (PVE 8)"
         run: |
           patch --dry-run --ignore-whitespace \