Guardian boss bars; Phase 7 approved

Adrian, 2026-11-03: guardians get a boss health bar like the Wither's, which
also leads players to them. Every player within 128 blocks of a living
guardian sees a red bar of their own (GuardianBars): name, zone, how many
blocks away, and HP. The End boss keeps the dragon's bar.
guardian_appears_and_returns checks the bar appears and goes once beaten.
Self-tests and the island check pass.

Phase 7 approved ("Then begin with the next phase"); README status updated.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

README.md

@@ -2,7 +2,7 @@
 
 A free NeoForge 1.21.1 modpack on Cobblemon 1.8: one large island with soft-gated, Palworld/ARK-style progression, plus a companion mod for the mechanics no addon covers. The plan is in [docs/roadmap.md](docs/roadmap.md); decisions taken so far are in [docs/design.md](docs/design.md).
 
-**Status:** Phases 0–6 approved (2026-11-02); Phase 7 (boss battles with area attacks) in progress. Checks per phase: `docs/checklists/`.
+**Status:** Phases 0–7 approved (2026-11-03); Phase 8 (questbook as a research tree, drop sources in JEI) in progress. Checks per phase: `docs/checklists/`.
 
 ## What's in the pack