Add extra buildings to in-app house purchase forms (RND-1965)

[hugokallstrom]

Summary

• Adds an extra-buildings collector (garage, shed, sauna, …) to the in-app vacation-home and villa purchase forms, copying the dialog UI from feature-movingflow's AddHouseInformationDestination.
• Each form submits the collected list in the existing priceIntentDataUpdate mutation, so returned offers reflect the declared buildings. 14 building types are hardcoded client-side with Lokalise TODO stubs (PriceIntent doesn't expose extraBuildingTypesV2).
• New shared file ExtraBuildingsSection.kt under feature-purchase-house/ui/extrabuildings/; no shared module extraction (deferred until there's a third consumer).

Stack

This PR builds on:

• Add in-app house (villa) purchase + Home picker dialog (RND-1965) #2949 — villa form (feat/in-app-house-purchase)
• Add in-app vacation home (fritidshus) purchase flow (RND-1965) #2947 — vacation home form (feat/in-app-vacation-home-purchase)

Spec / plan

• docs/superpowers/specs/2026-05-22-extra-buildings-in-house-purchase-design.md
• docs/superpowers/plans/2026-05-22-extra-buildings-in-house-purchase.md

Test plan

• :feature-purchase-house:ktlintCheck :feature-purchase-house:compileDebugKotlin green
• Emulator verified end-to-end: empty state → tap Add → dialog with all 14 types → select Garage / 25 m² / water on → Save → row appears as "Garage / 25 m² · Water connected" → tap X → row removed
• Submit a vacation-home form with one extra building and confirm the returned offer price differs from a submission without (sanity-check the serialization reaches the backend)
• Repeat the above on the villa form

Follow-ups (not in this PR)

• Replace English literals in ExtraBuildingsSection.kt with proper Lokalise keys for the 14 building-type display names (TODO comments mark each one)
• Consider extracting the section to a shared ui-extra-buildings module once / if a third consumer appears

🤖 Generated with Claude Code

[notion-workspace]

💶 Native purchase flows