feat: accessories module — optics, lights, suppressors, magazines

[crzykidd]

Major feature from PRD §10.6. Track gear alongside firearms, using the same ownership model as ammo and firearms.

Scope

• Track accessories: scopes, red dots, lights, grips, suppressors, magazines.
• Same owner_id + is_shared ownership model as ammo boxes and firearms.
• Optional attachment to a specific firearm.
• Detach/reattach history — track which firearm an accessory has been mounted on over time.
• Fields: type, make, model, serial (optional), purchase date, cost, notes.

Notes

• This is the home for magazine/capacity tracking at the accessory level — the per-firearm standard_capacity field tracks the design spec, not owned magazines.
• Largest of the roadmap items; likely its own phase with new tables + migration.

Source: PRD §10.6 (originally tagged v3.0).