fix(ui): wire up File menu actions and add .dat/.svg export

[aeronauty-flexcompute]

Summary

• File menu items (New NACA, Import .dat, Export .dat, Export SVG) were disabled placeholders — now fully functional
• New NACA opens the Airfoil Library panel; Import .dat triggers a file picker using the existing parser
• Export .dat downloads the current airfoil in standard Selig format; Export SVG downloads a vector graphic of the airfoil shape
• Bumps version to 1.1.1-dev with changelog entry

Changelog & Docs

• flexfoil-ui/src/lib/version.ts CHANGELOG updated
• All user-visible changes have a changelog entry
• New/changed docs pages added or updated in docs-site/docs/ — N/A, no new solver/API behavior
• No stale or aspirational content remains in affected docs

Test plan

• Open File > New NACA — should focus the Airfoil Library panel
• Open File > Import .dat — should open a file picker; importing a valid .dat loads the airfoil
• Open File > Export .dat — should download a .dat file with the current airfoil name and coordinates
• Open File > Export SVG — should download an .svg of the airfoil shape
• Verify the What's New dialog shows the 1.1.1-dev entry

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