Add per-parameter "visible in symbol" flag for KiCad EDA export

[Dant-hw]

Summary

Adds a per-part-parameter flag that controls whether an exported parameter is
shown on the schematic symbol in KiCad, i.e. the KiCad field's "visible"
attribute in the EDA HTTP-library API response.

Previously Part-DB always emitted parameter fields with "visible": "False",
so a parameter exported to KiCad was never displayed on the symbol without the
user manually toggling it in KiCad. This adds first-class control over that.

Two independent "visibilities"

The existing eda_visibility and the new eda_symbol_visibility do different
things and are deliberately independent:

Flag	Controls
eda_visibility (existing)	Whether the parameter is exported as a field at all
eda_symbol_visibility (new)	Whether that field is visible on the schematic symbol ("visible": "True"/"False")

The new flag only has an effect once the parameter is actually exported.

Behavior

• eda_symbol_visibility is a nullable tri-state on part parameters,
  mirroring the existing eda_visibility.
• When it is null, the new system default
  KiCadEDASettings::defaultParameterSymbolVisibility applies.
• Both default to false, so existing installations keep the previous
  behavior — exported parameter fields stay "visible": "False" until the
  flag (or the setting) is turned on. Fully backward compatible.

Changes

• Entity – new nullable eda_symbol_visibility column on AbstractParameter
  with accessors and matching serialization groups; multi-platform migration
  (MySQL / SQLite / PostgreSQL).
• Form – a second TriStateCheckboxType, shown for part parameters only.
• KiCadHelper – resolves the flag (explicit value, else the system default)
  and passes it to createField().
• Settings – defaultParameterSymbolVisibility (default false).
• Templates – new eye-icon column in the part edit Specifications table,
  next to the existing EDA-export column.
• Translations – English strings for the new tooltip and settings entries.
• Tests – assert "visible": "True" when the flag is set, and that the
  default stays "False".

Screenshot

Testing

• KiCadHelperTest passes (24 tests, 45 assertions), including the two new cases.
• Migration applies cleanly on SQLite; the eda_symbol_visibility column is
  created as expected.
• Smoke-tested in the Docker image: container boots, migration runs on startup,
  the new column is present, and the edit form renders the new column.

Notes

• Scope is part parameters only — orderdetails/supplier fields are not
  touched (could follow the same pattern later if wanted).
• Only messages.en.xlf is updated; other locales fall back to English until
  Crowdin syncs.

🤖 Generated with Claude Code

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 58.47%. Comparing base (a356b94) to head (5a785ab).
⚠️ Report is 1 commits behind head on master.

Additional details and impacted files

@@             Coverage Diff              @@
##             master    #1444      +/-   ##
============================================
- Coverage     58.48%   58.47%   -0.01%     
- Complexity     8707     8709       +2     
============================================
  Files           639      639              
  Lines         28146    28156      +10     
============================================
+ Hits          16461    16465       +4     
- Misses        11685    11691       +6     

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