Fix/export formats

[ulysse-bouchet-simvia]

Round of fixes and UX improvements for the .export editor: wider grammar coverage (base directories, unknown lines), three previously-dropped parameters, split basename/extension inputs, smarter defaults, and a reworked error/warning panel.

Added

• Base directory support — R extension name D/DC/RC unit lines are now parsed, formatted, and syntax-highlighted alongside standard F files, so .export files using the base type round-trip correctly.
• max_base, testlist, expected_diag parameters — the three remaining documented execution parameters are now first-class form fields. Multi-token P values (e.g. P testlist parallel validation code) are preserved end-to-end. testlist uses a structured selector (sequential/parallel + verification/validation + projects input, enabled only when validation is chosen). Optional parameters are omitted from the output when left blank.
• Separate file name and extension inputs — each file row now shows a basename field and an extension field joined by a visible ., so the extension can be prefilled from the chosen type while the basename stays easy to edit.
• Smarter default unit — when adding a file whose type isn't already present, the new unit is derived from the highest existing unit rounded up to the next multiple of 10 (e.g. 30 → 40) instead of defaulting to 0.
• "Unknown lines" preservation — lines the formatter can't interpret are now collected under a trailing # Unknown lines section instead of being dropped, and are highlighted as invalid in the syntax grammar so they stand out.

Changed

• Error and warning panels — merged into a single list showing every individual problem (per-field errors, missing-name, missing-extension, missing-type, bad unit, and form-level issues) with pluralized "Error(s)" / "Warning(s)" headers. Each row is clickable: errors jump to the offending input, warnings jump to a sensible anchor (rename → filename, missing mesh/rmed → the matching "Add" button, unit clash → the first offending file's unit input).
• Submit bar — the error/warning pills got a subtle tinted hover/focus background to feel clickable.

Fixed

• Entering text into the file name or extension inputs no longer silently reverts due to a state-sync feedback loop.
• Webview form fields no longer flag optional integer parameters as invalid when left empty.