0.4.0: NBT key fix + hub UI + /bns open + network hardening

Post-review fixes from the parallel code/security/hotkey/NPC audits.

## #35 — NBT keys (CRITICAL: screens were showing fictional data)
ServerEconomyBridge.pushBountySnapshot now reads the actual KubeJS keys:
- bnsBountyPool (compound id->1) — was bnsBounties.pool
- bnsBountyActive (compound id->{progress,target,reward,...}) — was bnsBounties.active
- bnsBountyCompleted (compound id->long cooldown-end-ms) — was bnsBounties.completed
- Filters completed by `cooldown-end > now` so old cooldowns drop off

ServerEconomyBridge.pushPlotSnapshot now reads server-scope state via
KubeJS's MinecraftServer mixin (kjs$getPersistentData) using reflection,
no compileOnly dep on KubeJS. Falls back to empty CompoundTag if the
method isn't there. Resolves owner names from PlayerList for online
players, GameProfileCache for offline.

## #36 — Hub UI + key rebind
Single primary key: B opens HubScreen. Direct shortcut keys (K/J/N/H/M)
all default to UNBOUND so they no longer compete with the ~100 other
pack mods. Audit found M = vanilla Social Interactions + FTB Chunks
fullscreen map (hard conflict, removed); H/N collided with Voice Chat
toggles (minor, removed); K/J were safe (kept rebindable for power users).

New HubScreen routes to the 5 sub-screens via labelled buttons + shows
tier/balance/fee at a glance in the header.

## #37 — /bns open <screen>
Java-registered Brigadier subcommand at RegisterCommandsEvent time,
merges with KubeJS's /bns root. New OpenScreenPacket (S2C) pushes a
screen open to the calling player. Screens: hub, tier, bounty, plot,
shop, questlog. Suggests valid screens via tab-complete.

This unlocks:
- Easy NPC dialogue COMMAND actions calling /bns open shop, etc.
- FTB Quests reward commands
- Command blocks / /trigger objectives
- Future scripted intros / tutorials

Also: patched /srv/fast/brass-sigil-server/server/config/easy_npc/
security.cfg to allow `bns` in executeAsUserCommandAllowList.ALL.

## #38 — Network hardening
- Per-player token bucket on C2S packets (10/s sustain, 20 burst).
- All STRING_UTF8 codecs capped: kind=8, args=80, which=16.
- Verb whitelist replaced with structured parse: args -> tokens ->
  per-verb regex validators -> rebuilt command. No more prefix-match
  surprises if /bns sell syntax expands.
- Per-player in-flight guard on tier upgrades (500ms) closes the
  double-spend race window.
- Bridge logs sanitised (control-char-stripped) so a hostile client
  can't inject newlines/ANSI into server logs.

## Review-driven nits also folded in
- Per-player tickCount (was shared static — N-player skew)
- VillagerTradeRebalance: try/catch around inner.getOffer; null cost-A
  passthrough; round-to-nearest denom split (was floor, ~10% price haircut)
- SpurHud caches Component refs (avoid 120/s allocation)
- ClientBnsState.completedIds now HashSet (O(1) per-frame lookups)
- BountyBoardScreen: deleted the empty `if (isActive)` dead branch
- Wire-format version bumped 0.2 -> 0.4 (added OpenScreenPacket)

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

gradle.properties

@@ -19,5 +19,5 @@ loader_version_range=[1,)
 mod_id=bnstoolkit
 mod_name=Brass and Sigil Toolkit
 mod_license=All Rights Reserved
-mod_version=0.3.1
+mod_version=0.4.0
 mod_group_id=uk.sijbers.bnstoolkit