Grouped accessories: parent/child model, location backfill, Device Manager UI

[manonstreet]

Summary

Apple's Find My data models accessory pairs (e.g. AirPods Pro) as a parent device in Devices.data plus N children in Items.data joined by groupIdentifier. FMS+ historically threw the relationship away — children surfaced as flat top-level entities ("Case", "Left Bud", "Right Bud") and parent groups appeared as a separate fourth entry, with no signal connecting them. Users with multiple pairs saw indistinguishable duplicates, and parent entities reported stale (isOld: true) locations even when their children had fresh GPS data (closes #10).

This change makes the parent/child relationship first-class:

• Parser (CacheDecryptor.parseDeviceArray): accepts a groupParentIDs map and stamps parentID onto child DevicePoints whose groupIdentifier resolves to a known parent.
• DevicePoint: gains a parentID: String? field, preserved through with().
• SyncEngine.readAndParseCaches: restructured into 4 phases — read+decrypt all caches into raw, build the parent map from Devices.data itemGroup entries, parse to DevicePoint with the map applied to items, then backfill any parent whose location is stale (isOld: true or older than the freshest child by ≥ 60 s) with the freshest child's lat/lon/accuracy.
• Posting layer: drops unaliased grouped children before posting. The parent group is the canonical entity for HA; sub-items only publish if the user has explicitly aliased them. Aliased children continue to publish — existing user setups keep working with zero migration.
• Device Manager UI: parent rows show a hover-revealed disclosure pill (accent-blue chevron in a faint pill) on the right; clicking expands to indented children. Aliased grouped parents stay visible in the Unassigned list with a green "Assigned" badge and disabled "Assign" button — chevron still works so users can drill in and alias individual buds (e.g. for finding a lost one).
• Bumps MARKETING_VERSION to 1.4.0b — this is a feature line, not a patch.

Backward compatibility

• Existing aliases keep working. Aliased UUIDs (parent or child) continue to publish exactly as before.
• No settings migration. hideGroupedChildren was prototyped, then dropped — the per-parent disclosure pill plus the unconditional posting filter cover both UI hide and posting concerns more cleanly than a global toggle.

Test plan

• 70 unit tests across 5 files, all passing — including:
  • parentID plumbing on DevicePoint, parser, with()
  • filterUnaliasedGroupedChildren: keeps parents, drops unaliased children, keeps aliased children, ignores ungrouped items
  • backfillParentLocations: replaces isOld parent location, leaves fresh parent alone, replaces parent older than child by ≥ 60 s, no-op when no children
• Manual: live AirPods Pro pair on Apple Silicon — parent shows in Device Manager with chevron, expanding shows Case/Left/Right indented; backfilled parent location matches the freshest child's; existing AirPods alias still publishes; aliasing the parent leaves it visible with the "Assigned" badge.

Documentation

• Docs/DEVICE-MANAGEMENT.md — new "Grouped Accessories" section
• CLAUDE.md — test count, parentID note, convention line
• README.md — Features bullet