M0: scaffold bnstoolkit mod (NeoForge 1.21.1)

Empty mod that loads cleanly on client + dedicated server. Sets up the
package layout and milestone TODOs for the BNS in-game UI work.

- uk.sijbers.bnstoolkit.{BnsToolkit, BnsToolkitClient} mod entries
- 5 placeholder screens extending a shared BaseBnsScreen
  (TierUpgrade, BountyBoard, QuestLog, PlotPurchase, ShopBrowser)
- 3 key bindings (T/B/P) registered, handlers TODO M1+
- SpurHud overlay placeholder for M4
- Network: payload registrar + one smoke-test C2S/S2C pair
  (RequestTierState / TierStateUpdate)
- en_us.json for screen + keybind labels
- neoforge.mods.toml pinned to neo_version 21.1.228 (live server match)

Build verified: ./gradlew build -> bnstoolkit-0.1.0.jar (15.6 KB).

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

gradle.properties

@@ -0,0 +1,23 @@
+# Sets default memory used for gradle commands. Can be overridden by user or command line properties.
+org.gradle.jvmargs=-Xmx2G
+org.gradle.daemon=true
+org.gradle.parallel=true
+org.gradle.caching=true
+org.gradle.configuration-cache=true
+
+# Parchment mappings (parameter names + javadocs)
+parchment_minecraft_version=1.21.1
+parchment_mappings_version=2024.11.17
+
+# Environment Properties — must match the live BNS server
+minecraft_version=1.21.1
+minecraft_version_range=[1.21.1]
+neo_version=21.1.228
+loader_version_range=[1,)
+
+## Mod Properties
+mod_id=bnstoolkit
+mod_name=Brass and Sigil Toolkit
+mod_license=All Rights Reserved
+mod_version=0.1.0
+mod_group_id=uk.sijbers.bnstoolkit