Schema-driven UI and worker dispatch by converter id

[fedyunin]

Summary

Stops the UI from knowing about individual converters. Worker dispatches by converterId to whatever is in the registry; the renderer builds its options form from each converter's declarative options[] schema. Adding a new format is now: one folder under src/core/converters/, one test fixture, one entry in the registry — and it appears in the desktop app automatically.

Stacked on top of #2.

What changed

Renderer

• New Converter card with a dropdown of registered converters and a per-converter description line.
• Options card is now empty in HTML and populated dynamically from the selected converter's schema (boolean → checkbox, enum → select, number → number input, string → text). Saved per converter — switching direction keeps each one's last values.
• File picker and drop-zone filters use the current converter's inputs.extensions (e.g. .mif/.mid for mif-to-xlsx, .kml/.kmz for kml-to-mif).
• All converter-specific HTML and JS for the Excel exporter is gone — the same form generator handles both shipped converters.

Worker / IPC

• worker.js now dispatches converters.get(id).run({inputs, output, options}, ctx). Runs converters.validateOptions() before invocation; surfaces option errors as a fatal error message.
• main.js exposes converters:list returning a lean serializable view of the registry. selectFiles accepts the current converter's allowed extensions for native dialog filters.
• preload.js exposes listConverters() and the extension-aware selectFiles(options).
• convert:start payload moved from {inputMode, inputFolder, selectedFiles, recursive, paintRows, ...} to the contract-aligned {converterId, inputs, output, options}.

Settings (v2 with migration)

{
  "version": 2,
  "language": "en",
  "inputMode": "folder",
  "inputFolder": "...",
  "outputFolder": "...",
  "selectedFiles": [],
  "converterId": "kml-to-mif",
  "converterOptions": {
    "mif-to-xlsx": { "paintRows": true, "skipBlack": true, /* ... */ },
    "kml-to-mif": { "flat": false, "charset": "WindowsCyrillic" }
  }
}

migrate() lifts legacy flat option keys into converterOptions['mif-to-xlsx'] so existing 1.0.x users see no behavior change after the upgrade. saveSettings always stamps the current version so future migrations can branch on it.

i18n

New shared keys (section.converter, field.converter, hint.optionsEmpty); the subtitle and drop hint are now format-agnostic. EN / RU / KK updated. Per-option labels currently come straight from the schema (English) — a follow-up PR can add an optional i18nKey on options without touching the renderer.

Tests

81 passing (75 from #2 + 6 new settings migration tests):

• defaults are on the current version with the new shape
• migrate lifts every legacy flat key into converterOptions['mif-to-xlsx']
• migrate of already-current settings preserves everything and returns a fresh copy
• migrate returns defaults on garbage input
• round-trip writes the version field; loadSettings on a v1 file auto-migrates

Renderer is browser-only JS — validated by node --check. Real smoke test is manual:

npm run dev
# Pick "MapInfo → Excel/CSV", convert a folder, confirm output matches 1.0.4
# Switch to "KML/KMZ → MapInfo MIF/MID", convert the Karaganda KMZ, confirm 9 layers / 1854 features

Test plan

• npm test is green (81)
• node --check on every JS file
• manual: open the app, both converters render their options panels from the schema
• manual: settings.json from 1.0.4 in app.getPath('userData') loads with identical behavior
• manual: each converter remembers its own options after switching back and forth

Follow-ups

• feat/cli — bin/mifkit convert <id> <input> <output> --flag=value over the same registry. Schema validation already covers CLI flag parsing.
• feat/i18n-options — optional i18nKey on option definitions so option labels can be translated without renderer changes.
• feat/mif-to-kml — reverse direction (MapInfo → Google Earth).

🤖 Generated with Claude Code

[fedyunin]

Superseded by #5 after the stacked base chain broke when #1 was merged. All commits from this PR are present in #5.