Add European Portuguese (pt-PT) translation

[pdlourenco]

Summary

Adds a complete European Portuguese (pt-PT) localisation, following the process in docs/i18n.md and the pattern of previous language PRs (#145 Italian, #157 Hungarian, #181 Finnish, #206 German).

• messages/pt-PT.json — all 707 messages translated into European Portuguese (pt-PT specifically — gasóleo, GPL, matrícula, palavra-passe, ficheiro, definições…), reviewed by a native speaker
• project.inlang/settings.json — pt-PT registered in locales and languageTags
• SettingsModal.svelte — adds the Português (Portugal) label to the locale dropdown, and also adds the previously missing Finnish label (Suomi, currently rendered as "FI")

Validation

• Key set and key order identical to messages/en.json (707/707)
• Every {placeholder} preserved verbatim (checked programmatically)
• pnpm build passes; the compiled Paraglide runtime includes pt-PT with the translated variants
• pnpm lint clean on the changed files

Notes

• Sentence case is used for labels/buttons per pt-PT UI conventions (Portuguese capitalises far less than English)
• Terms were kept country-neutral (e.g. "certificado de emissões", "centro de inspeção") rather than Portugal-specific regulatory names
• While the first draft of the translation was generated by Claude, I (human) reviewed it manually and also with Claude Fable.

[pdlourenco]

Note: after rebasing onto current dev (the i18n restructure and the new
Compliance/vehicle-hub/reports features), 214 new strings were added to the
translation beyond the ~600 that were already native-reviewed. I'm reviewing
those new strings now — converting to draft until that's done, should be ready
within a few days. The rest of the file is final.

[pdlourenco]

Reviewed the new additions and corrected the translation.
Should be ready to merge.