Phase 7d: Print API + QR Print Tab + Hangar Plugin (foundation MVP)

[strausmann]

Master tracking for Phase 7d implementation. Spec under review in the PR for branch `docs/phase-7d-foundation-spec`.

Scope (per spec)

Backend

• POST /api/preview + POST /api/print with γ-hybrid PrintItem schema (name/subtitle/qr_url/image_url/copies/extras)
• Tape-match logic with force-override + audit flag
• Multi-item × copies → N Job rows
• Alembic migration: Job table gains `api_key_id`, `source_ip`, `tape_match_override`, `plugin`, `plugin_item_id`

Plugin protocol

• IntegrationPlugin.search(query, limit) → list[PluginItemSummary]
• IntegrationPlugin.get_item(item_id) → PluginItem
• Optional HasChildren.get_children(item_id) → list[PluginItemSummary]

Plugins

• Grocy, SnipeIt, Spoolman: gain search() + get_item()
• Hangar: new plugin module `backend/app/integrations/hangar/` with all 3 methods + httpx client

Frontend

• New HTMX route `/qr-print` with platform-toggle, search-debounce, results-list, select-form
• Per-item copies input
• Children-toggle for hierarchical items
• Live preview with red/green tape-match border + tape badge top-right
• Print-button → toast with job IDs

Dependencies

• Phase 7c API-Auth (Phase 7c: App-side API-Authentifizierung (multi-key, scoped, audit-trail) #78) — hard-required for production
• strausmann/hangar#63 (cross-app) — Hangar must ship its print-page + 3 API endpoints
• Phase 7b.1 (fix(api): Phase 7b.1 — upsert name-collision + /readiness proxy gap #77) currently merging in parallel

Out-of-scope (Phase 7e+)

• Aggregations templates (one big label for whole shelf)
• Per-plugin search filters
• Saved searches/favourites
• Plugin config via UI
• Multi-printer fan-out
• Image rendering on labels (renderer falls back to QR-only for now)

Acceptance criteria

See spec Section 13 "Definition of Done for Phase 7d".

Refs #22