pack: KubeJS tidying + admin commands, bump to 0.20.0

Tidying pass on the KubeJS suite before plot system V1 lands. Sets up
the file structure + conventions + diagnostics so the larger plot
system has a clean foundation.

Changes:

1. NEW kubejs/README.md
   File layout doc + conventions: logging prefix [bns/<module>],
   persistent-data key naming (bns* prefix), one concern per file,
   performance discipline (O(1) lookups, no polling).

2. Split economy_policy.js -> recipes_waystones.js + recipes_numismatics.js
   Single-concern files. recipes_waystones removes ALL waystones
   crafting (welcome.js distributes the only allowed waystone instead).
   recipes_numismatics removes the 5 coin-denomination crafts.

3. NEW kubejs/server_scripts/bns_admin.js
   /bns admin subcommands for OP diagnostics:
     - info                       calling player's flags+counts
     - waystone-count <player>    read stored count
     - waystone-set <player> <n>  override stored count
     - reset-welcome <player>     clear bnsWelcomeGranted -- replays
                                  the welcome grant on next login
   Registered via ServerEvents.commandRegistry with Brigadier tree,
   permission level 2 (OP). No performance cost (operator-triggered only).

4. Logging added to waystones_policy.js + welcome.js
   Every action prints `[bns/<module>] ...` so server logs can be
   filtered with `journalctl ... | grep '\[bns/'`.

Performance discipline applied:
- All event-handler lookups use Set.has (O(1)), not Array.includes
- No periodic tick polling anywhere
- No network calls in event handlers
- console.info is cheap (no string format unless logged)

Bumps to 0.20.0. Plot system V1 follows in v0.21.x as a separate
multi-file submodule under server_scripts/plots/.

pack/overrides/kubejs/server_scripts/bns_admin.js

@@ -0,0 +1,89 @@
+// Brass & Sigil — admin commands (/bns admin ...)
+//
+// Diagnostic + maintenance commands for OPs. Players without OP level
+// (>= 2) get a permission-denied response from the command framework.
+//
+// Subcommand summary:
+//   /bns admin info                       state of the calling player
+//   /bns admin waystone-count <player>    read stored count
+//   /bns admin waystone-set  <player> <n> override stored count
+//   /bns admin reset-welcome <player>     clear bnsWelcomeGranted flag
+//                                         so the welcome grant fires again
+//
+// Adding new subcommands: follow the same `Commands.literal(...)
+// .then(...)` pattern below. Keep handlers cheap -- these are only run
+// on operator action so performance isn't critical, but make them
+// readable.
+
+ServerEvents.commandRegistry(event => {
+    const { commands: Commands, arguments: Arguments } = event;
+
+    const bnsAdmin = Commands.literal('bns')
+        .then(Commands.literal('admin')
+            .requires(src => src.hasPermission(2))
+
+            // /bns admin info
+            .then(Commands.literal('info').executes(ctx => {
+                const player = ctx.source.player;
+                if (!player) {
+                    ctx.source.sendSystemMessage(Text.red('Run from a player context.'));
+                    return 0;
+                }
+                const data = player.persistentData;
+                const lines = [
+                    `Player: ${player.username} (${player.uuid})`,
+                    `bnsWaystoneCount  = ${data.getInt('bnsWaystoneCount')}`,
+                    `bnsWelcomeGranted = ${data.getBoolean('bnsWelcomeGranted')}`,
+                ];
+                lines.forEach(line => ctx.source.sendSystemMessage(Text.aqua(line)));
+                console.info(`[bns/admin] info: ${player.username} -> ${JSON.stringify({
+                    waystones: data.getInt('bnsWaystoneCount'),
+                    welcomed: data.getBoolean('bnsWelcomeGranted'),
+                })}`);
+                return 1;
+            }))
+
+            // /bns admin waystone-count <player>
+            .then(Commands.literal('waystone-count')
+                .then(Commands.argument('target', Arguments.PLAYER.create(event))
+                    .executes(ctx => {
+                        const target = Arguments.PLAYER.getResult(ctx, 'target');
+                        const count = target.persistentData.getInt('bnsWaystoneCount');
+                        ctx.source.sendSystemMessage(Text.aqua(
+                            `${target.username} has bnsWaystoneCount = ${count}`
+                        ));
+                        return 1;
+                    })))
+
+            // /bns admin waystone-set <player> <n>
+            .then(Commands.literal('waystone-set')
+                .then(Commands.argument('target', Arguments.PLAYER.create(event))
+                    .then(Commands.argument('count', Arguments.INTEGER.create(event, 0, 1000))
+                        .executes(ctx => {
+                            const target = Arguments.PLAYER.getResult(ctx, 'target');
+                            const count = Arguments.INTEGER.getResult(ctx, 'count');
+                            target.persistentData.putInt('bnsWaystoneCount', count);
+                            ctx.source.sendSystemMessage(Text.gold(
+                                `Set ${target.username}'s bnsWaystoneCount = ${count}`
+                            ));
+                            console.info(`[bns/admin] waystone-set: ${target.username} -> ${count}`);
+                            return 1;
+                        }))))
+
+            // /bns admin reset-welcome <player>
+            .then(Commands.literal('reset-welcome')
+                .then(Commands.argument('target', Arguments.PLAYER.create(event))
+                    .executes(ctx => {
+                        const target = Arguments.PLAYER.getResult(ctx, 'target');
+                        target.persistentData.putBoolean('bnsWelcomeGranted', false);
+                        ctx.source.sendSystemMessage(Text.gold(
+                            `Cleared bnsWelcomeGranted for ${target.username}. ` +
+                            `They'll get the welcome packet again on next login.`
+                        ));
+                        console.info(`[bns/admin] reset-welcome: ${target.username}`);
+                        return 1;
+                    })))
+        );
+
+    event.register(bnsAdmin);
+});