feat: format empty partitions on system disk (v0.32.6)

Detect and offer to format empty (no filesystem) partitions on the system
disk. Adds IsSystemPartition() for granular per-partition safety checks
instead of blocking the entire system disk. Init wizard shows formatable
partitions with appropriate warnings. Add felhotest demo node to docs.

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

CHANGELOG.md

@@ -1,5 +1,17 @@
 ## Changelog
 
+### v0.32.6 — Format empty partitions on system disk (2026-02-27)
+
+#### Added
+- **storage/scan.go**: New `FormatablePartition` struct and `FormatablePartitions` field on `ScanResult` — detects empty (no filesystem), unmounted, non-system partitions on system disks
+- **storage/scan_linux.go**: New `getSystemPartitionPaths()` resolves actual system partition device paths from fstab (more granular than `getSystemDiskNames()` which returns parent disk names). `ScanDisks()` now populates `FormatablePartitions` after enrichment
+- **storage/safety_linux.go**: New `IsSystemPartition()` — checks if a specific partition is a system partition (/, /boot, /boot/efi, swap) or is currently mounted; more granular than `IsSystemDisk()` which blocks the entire disk
+- **web/storage_handlers.go**: Scan API response now includes `formatable_partitions` array
+- **web/templates/storage_init.html**: Init wizard shows formatable system-disk partitions as a separate selectable section with info banner, conditional warning text, and hidden partitioning progress step
+
+#### Changed
+- **storage/format_linux.go**: `FormatAndMount()` now uses `IsSystemPartition()` for partition-only operations (`CreatePartition=false`) instead of `IsSystemDisk()` — allows formatting empty data partitions on the system disk while still blocking system partitions
+
 ### v0.32.5 — USB badge fix + graceful Tier2 backup on disconnected/inactive/removed destinations (2026-02-27)
 
 #### Fixed