fix: reading a book no longer freezes a moving train

[bh679]

Summary

Reading a written book in singleplayer on the moving Sable train made the carriage group under the player's feet (plus neighbours) vanish ~1 s later, returning only on a world reload.

Root cause: DT's books open the vanilla BookViewScreen, which inherits Screen.isPauseScreen() (defaults to true) without overriding it (confirmed via javap). Opening a book pauses singleplayer → triggers a full autosave → Sable's saveAll() shuffles the train's sub-levels through holding chunks, and the resume (book close) fails to restore the sub-levels around the player (Attempted to snatch sub-level … wasn't present in the holding chunk / Received a sub-level movement packet for a non-existent sub-level), vanishing the carriages.

This adds the isPauseScreen() → false override Mojang omitted, via a client mixin, so reading a book no longer pauses/autosaves a run mid-ride — the train keeps moving while you read.

Implemented as an additive method merge, not @Inject: since BookViewScreen doesn't declare isPauseScreen() (it's inherited from Screen), an @Inject targeting BookViewScreen would fail to resolve at apply-time and crash on load.

Scope / trade-off

• Affects all written-book reads in singleplayer (starting, chest, story books). Intended.
• No multiplayer effect — MP never pauses on a screen.
• Behaviour change: the world keeps ticking while reading, so the player can take damage / be attacked mid-read (arguably more correct on a constantly-moving roguelite train).
• Out of scope: ESC-menu / advancement-popup pauses can still cause the same Sable desync — the durable Sable-side fix is a separate task.

Mod impact

One new client mixin. No new deps, no MC/NeoForge/Sable bump, no new blocks/items/entities, no world-gen or networking changes.

Changes

• src/main/java/games/brennan/dungeontrain/mixin/client/BookViewScreenNoPauseMixin.java (new)
• src/main/resources/dungeontrain.mixins.json (register client.BookViewScreenNoPauseMixin)
• gradle.properties mod_version 0.367.0 → 0.368.0
• .github/release-notes/changelog.json (player-facing fix entry)

Test plan

• ./gradlew build — pass; build/libs/dungeontrain-0.368.0.jar (8.3 MB)
• Unit tests — 924/924 pass (98 suites, 0 failed)
• ./gradlew runClient — launches clean; log confirms the mixin applies into BookViewScreen with no apply error
• In-game (Sable train): open a book on the moving train → no Saving and pausing game… on open, no Sable snatch/holding-chunk errors on close, no carriages vanish, train keeps moving

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