feat(bridge): boss frames for the site's public triggers (runicnpc stage 6)

npc.boss.spawned, npc.boss.phase and npc.boss.died, from RunicNPC
API 5's boss hooks, for the site's spawned, phase and killed triggers
(D277). The death frame names the killer and counts the players who
hurt the boss; npc.died still carries every contributor.

A profile's `boss` and `use` blocks travel in the push unchanged.
runicnpc_api and RunicNpcApiNeeded are 5.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01E14m6SuuY6i1vASFeGDBeY

overlay.toml

@@ -80,7 +80,7 @@ requires_plugins = ["Kits", "ZoneManager"]
 
 # ── The RunicNPC API the bridge needs ───────────────────────────────────────
 #
-# RunicNPC (docs/runicnpc/PLAN.md stages 4 and 5): the bridge's npc.* commands call
+# RunicNPC (docs/runicnpc/PLAN.md stages 4 to 6): the bridge's npc.* commands call
 # RunicNPC's API and need at least this version of it. It MUST equal
 # `RunicNpcApiNeeded` in RunicGateway.cs; `node scripts/checkPlugin.js` holds the
 # two equal. The release copies it into manifest.json, and the installer's
@@ -88,4 +88,4 @@ requires_plugins = ["Kits", "ZoneManager"]
 #
 # RunicNPC is optional to the bridge until its stage 9: without it every npc.*
 # command answers `runicnpc-missing`, and events place Rust's own scientists.
-runicnpc_api = 4
+runicnpc_api = 5