Add Air Temple cartographer maps

[xefensor]

Summary

Adds an initial in-world discovery path for the Air Temple. After Stage 2 begins, journeyman-or-higher cartographers sell an Air Temple Explorer Map for 12 emeralds and a compass. The map uses an exact target X for the nearest retold:air_temple.

The offer is appended lazily during server-side villager interaction so cartographers with saved offers from before the stage transition keep those trades and gain the new map without rerolling their profession. Failed structure searches are throttled per cartographer, and duplicate Air Temple map offers are prevented.

Updates the public roadmap, changelog, architecture/status documentation, and design-risk tracking. This implements the initial cartographer path discussed in #11 while leaving wider seed and upgraded-world retrogen verification visible.

Player or developer impact

Players gain a survival-friendly way to find the Stage 2 Air Temple without using /locate. Existing cartographers remain compatible, and the trade is unavailable during Stage 1.

Developers gain a data-driven structure destination tag and deterministic GameTest coverage for stage gating, saved-offer preservation, costs, exact marker coordinates, and duplicate prevention.

Validation

• ./gradlew build
• ./gradlew runGameTestServer, when relevant
• Focused in-game testing, when relevant
• Dedicated-server or multiplayer testing, when relevant

All 20 required GameTests passed. The developer verified the basic cartographer interaction and exact-map behavior in-game on 2026-07-22.

Still pending: wider multi-seed coverage, edited upgraded-world retrogen destinations, real dedicated-server interaction, and multiplayer purchases. One GameTest run also showed a brief vanilla-style map-rendering stall, which is recorded in the design-risk tracker for profiling.

AI assistance

• I reviewed and understand all submitted changes, including AI-assisted output.

Codex assisted with repository/GitHub triage, implementation, tests, and documentation. The result was validated with the complete Gradle build, the GameTest server, diff checks, and developer in-game confirmation.

Documentation and release notes

• Updated CHANGELOG.md for player-facing or notable technical changes
• Updated README or system documentation when behavior or architecture changed
• Added or updated tests where practical

Visual evidence

No screenshot or video was captured. The developer confirmed the basic exact-map behavior in-game.

Licensing

• I have the right to contribute every included file.
• Code and non-asset contributions are provided under LICENSE-CODE.md.
• I discussed creative-asset contributions with the developer before including them.

No creative assets are included in this PR.