feat(settings): Create Extra Fields by Formula via built-in JSON editor

[akira69]

Now addressed in PR #885

Summary

This PR adds Formula Extra Fields as a user-facing workflow in Settings so people can create reusable calculated values from existing fields without changing stored source data.

In practical use, this helps users build cleaner dates, usage deltas, cost math, and template-ready derived values directly in the app.

betterbugs_recording.webm

User-Facing Outcomes

• Create per-entity formula fields (Spool, Filament, Manufacturer).
• Author formulas with a JSON Logic editor and token groups (Operators, Helper Functions, Field References).
• Validate formulas with sample values and preview before saving.
• Control where each formula appears: Show, List, Template.
• Optionally allow list-surface formulas to participate in Hide Columns toggling.
• Expose selected formula fields in API derived payloads as derived.<key>.

What Changed

1) Formula Authoring Workflow

• Adds Formula Extra Fields as a first-class workflow in Extra Fields settings.
• Uses token-based JSON insertion for faster authoring and fewer syntax mistakes.
• Supports helper-first insertion with compatibility hints and placeholder insertion.

2) create/edit formula field flow

• new "formula extra fields" section under the "Extra Fields" Settings

- Formula Extra Field Edit Page (simple) - Expandable/Collapsable Sections for Clickable Operators, Helper Functions and Field References with considerate layout density - Type-Aware and clickable functions to fill JSON

3) Editor + Help UX

• dark-mode multi-line selection visibility in the JSON editor.

- Aligned help/settings documentation with formula-focused guidance and terminology.

4) Template/List/API Integration

• Template-enabled formula fields are available to templates as derived values.
• List-surface formulas can opt into Hide Columns visibility toggling.
• API inclusion is field-level via include_in_api, exposed under derived.<key> when derived output is requested.

• template usage example using {derived.your_key}

• API response snippet with derived payload

Validation

• Python syntax check passed for touched backend files.
• Frontend production build passed (npm ci && npm run build in Dockerized Node build environment).
• Local Docker runtime verified on port 8874 with successful probe.

Scope Notes

• Formula-focused scope in this PR.
• Complex framework is tracked separately in #878.

Upstream Issue / Feature Request Mapping

Fully Addressed

• Fixes Display HEX value on Filament Details page #568
  • Filament formulas can now expose color_hex on Filament detail and list surfaces, with optional list column toggle behavior.

Partially Addressed by Formula Framework

• Refs Labels: Date formatting #795
  • Date-only output is now possible via date_only(...) for labels/templates; local-timezone rendering is still out of scope.
• Refs Sorting spool list by extra-field #600
  • “Time since last dried” style derived fields are now possible, but sorting by extra/derived fields is not added in this PR.
• Refs Tracking weight to monitor moisture content? #609
  • Moisture-related calculated fields are now possible, but no dedicated weigh/track modal workflow is added.
• Refs Automatically Calculate Remaining Weight when entering a spool #569
  • Gross/remaining/value-style calculations are now possible as derived outputs, but this PR does not write back canonical remaining_weight from gross-weight input.
• Refs Add ability to sort by hue #853
  • hue_from_hex(...) enables derived hue values, but click-to-sort by hue is not implemented here.
• Refs Some feature requests after using for several months #430
  • This framework supports formula-based linked/calculated field outputs, but the broader multi-request issue remains only partially covered.

Formula-Resolvable Requests (No Dedicated Issue Found)

• Time since purchase: {"days_between": [{"var": "created_at"}, {"today": []}]}
• Remaining value estimate: {"*": [{"var": "price"}, {"/": [{"var": "remaining_weight"}, {"var": "weight"}]}]}

Additional Drying Context

• Refs Add support for tracking drying of spools #711
  • Custom extra fields plus formula fields can model parts of the drying-tracking workflow, such as storing a manual last_dried timestamp and deriving time-since-last-dried, but this PR does not add first-class drying fields or dedicated drying UI.