v0.15.0: Attach existing drive wizard (bind mount, no format)

New Settings wizard to attach drives with existing filesystems without
formatting. Mounts partition at staging path, lets user browse and pick
a subfolder, then bind-mounts it at /mnt/<name> with fstab entries.

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

CHANGELOG.md

@@ -1,5 +1,17 @@
 ## Changelog
 
+### What was just completed (2026-02-18 session 50)
+- **v0.15.0 — Attach Existing Drive (bind mount wizard):**
+
+  New feature: Settings → "Meglévő meghajtó csatolása" wizard. Allows attaching a drive that already has a filesystem (ext4, etc.) without formatting. Solves the real-world scenario where a customer's drive contains existing data that must be preserved.
+
+  **How it works:** The partition is mounted read-only at a hidden staging path (`/mnt/.felhom-raw/<label>`). A directory browser lets the user navigate the drive's contents and create a new folder. The selected folder is bind-mounted at `/mnt/<hdd-name>`, keeping the controller's data isolated from existing files. Two fstab entries (raw + bind, both with `nofail`) ensure the mount survives reboots.
+
+  **Wizard flow:** Scan → Select partition (only shows partitions with existing FS) → Mount raw + Browse directories → Create folder if needed → Configure mount name + label → Finalize (bind mount + fstab + permissions + register). Cancel cleans up the temp mount.
+
+  **New files (4):** `internal/storage/attach.go`, `internal/storage/attach_linux.go`, `internal/storage/attach_other.go`, `internal/web/templates/storage_attach.html`
+  **Modified files (3):** `internal/web/storage_handlers.go` (6 new API handlers), `internal/web/server.go` (route + activeRawMount field), `internal/web/templates/settings.html` (button)
+
 ### What was just completed (2026-02-18 session 49)
 - **v0.14.2 — Backup Bug Fixes (4 fixes from code review):**