Summary

• Wire up document attachments on service log entries, maintenance items, quotes, and vendors by adding a "Docs" drilldown column with per-entity document counts
• Add serviceLogDocumentDef, maintenanceDocumentDef, quoteDocumentDef, and vendorDocumentDef detail definitions with routing
• Introduce a formKind discriminator on detailRoute so nested detail views (e.g. appliance -> maintenance -> docs) route to the correct document def instead of the parent tab's; nil handler is treated as "no match" to prevent fallback surprises
• Extract entityIDs generic helper to replace repeated manual ID-collection boilerplate in handlers
• Scoped variants (appliance maintenance, vendor quotes, project quotes) and their handlers are also updated
• All changes follow the existing pattern used by projects, appliances, and incidents -- no data-layer changes needed

Steps to reproduce

1. Open the Maintenance tab, select a maintenance item, drill into Service Log, select an entry, and activate the "Docs" column to see its documents
2. Go back to the Maintenance tab and activate the "Docs" column directly on a maintenance item
3. Open the Quotes tab and activate the "Docs" column on a quote
4. Open the Vendors tab and activate the "Docs" column on a vendor
5. For nested paths (e.g. Appliances -> drill into appliance -> Maint -> drill into item -> Docs), verify the breadcrumb says "Maintenance" not "Appliances"

closes #427