feat(settings): Applications Framework for Optional Extensible Features

[akira69]

Summary

Introduces the Applications Framework — infrastructure for optional, user-configurable applications that extend Spoolman without modifying core code.

Rebrands "Complex Fields" to "Applications" — a more user-familiar ecosystem paradigm. The framework is independent: it merges standalone with a demo registry, and future features build on top without modifying core Spoolman.

Development note: Active development is on the fork PR akira69/Spoolman_Labels#9. This upstream PR will be updated when ready for review.

Architecture

• Registry pattern: register_application() at startup, runtime dict, DB persistence for enabled state
• Per-entity control: Separate enabled/disabled toggles per Spool / Filament / Vendor surface
• Independence: No other PRs required to merge; future features optionally register as applications

What Changed

Backend

• spoolman/applications.py (NEW) — ApplicationDefinition, ApplicationSurface, registry, enable/disable logic
• spoolman/demo_applications.py (NEW) — 8 concept stubs registered at startup (Drying Tracker, Inventory Alerts, Print History, Weight Audit, QR Customization, Spool Count, Filament Textures, Storage Conditions)
• spoolman/api/v1/field.py (MODIFIED) — endpoints renamed to /field/application/{entity_type} (GET/POST)
• spoolman/settings.py (MODIFIED) — setting keys updated to applications_* (was complex_fields_*)
• spoolman/complex_fields.py (DELETED) — replaced by applications.py
• migrations/versions/…_rename_complex_fields_to_applications.py (NEW) — Alembic upgrade/downgrade for setting key rename

Frontend

• client/src/components/applicationCard.tsx (NEW) — Card with emoji avatar, per-surface enable toggles, Configure button
• client/src/pages/applications/index.tsx (NEW) — Catalog page with Segmented filter (All/Enabled), responsive grid
• client/src/pages/applications/detail/index.tsx (NEW) — Detail page with surface table and enable switches
• client/src/utils/queryFields.ts (MODIFIED) — types/hooks/API paths renamed to Applications
• client/src/App.tsx (MODIFIED) — Applications resource + /applications and /applications/:appKey routes added
• client/src/pages/settings/index.tsx (MODIFIED) — Complex Fields menu removed
• client/src/pages/settings/complexFieldsSettings.tsx (DELETED)
• client/public/locales/en/common.json (MODIFIED) — i18n keys updated

Code Quality Compliance ✅

• ✅ ESLint: 0 errors across all modified/new frontend files
• ✅ Prettier: All files formatted
• ✅ Ruff: Fixed FBT001 (boolean positional arg → keyword-only), E501 (long lines wrapped with implicit string concatenation)
• ✅ Pre-commit: Full suite passed (ESLint, Prettier, Ruff, UV lockfile)

Next Steps

• Phase 2: First real application — Spool Count (Number of spools in filament overview #746) as proof-of-concept implementation
• Optional: PR feat(settings): Create Extra Fields by Formula via built-in JSON editor #885 (Formula Fields) and other features can optionally register as applications

Test Checklist

• Applications entry appears in sidebar navigation
• /applications catalog page loads with 8 demo app cards
• Each card shows emoji icon, name, description, and per-surface enable toggles
• Toggling a surface enable/disable persists after page reload
• Segmented filter (All / Enabled) correctly filters the grid
• Clicking Configure navigates to /applications/:appKey detail page
• Detail page shows table with all surfaces and enable switches
• Back button returns to catalog from detail page
• Settings page no longer shows Complex Fields section
• API: GET /api/v1/field/application/spool returns demo apps