docs(earth): 📝 Update Earth world developer notes and gameplay guidelines with mechanics, design considerations, and implementation details

Co-Authored-By: Lilith Autocommit <noreply@atlilith.com>

src/resources/worlds/earth/dev-notes.md

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+# Earth — Developer Notes
+
+## Overview
+The primary simulation archetype. Full climate physics: water cycle, weather events, ecology,
+volcanism. This is the most developed world — all other fictional homeworlds reference it.
+
+## Physics Features
+- `water_cycle: true` — precipitation, runoff, river formation, lake evaporation
+- `weather_events: true` — storm systems, drought, seasonal variation
+- `ecology: true` — flora succession (pioneer → canopy), fauna habitat tracking
+- `volcanism: true` — tectonic activity, eruption events
+- `co2_cycle: false` — atmospheric CO2 feedback not yet implemented
+- `dust_storms: false` — reserved for Mars archetype
+- `acid_clouds: false` — reserved for Venus archetype
+
+## Biome Subscriptions
+Subscribes to all standard collections: aquatic, arctic, temperate, tropical, elevated,
+wetland, geological. This gives the widest biome variety.
+
+## Climate Parameters
+See `climate_params.json` for all 17 tunable parameters. Key values:
+- Default grid: 40×24 (duel size), 2 polar rows
+- `wind_conductivity`, `energy_scale`, `evaporation_rate` are the most sensitive tuning knobs
+
+## Build Notes
+- `runtime_biomes.json` is generated/maintained alongside the biome classifier in mc-climate
+- `hydrology_params.json` controls river formation thresholds and lake persistence

src/resources/worlds/earth/gameplay-notes.md

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+# Earth — Gameplay Notes
+
+The baseline world archetype. A temperate planet with oceans, continents, rivers, and a full
+living biosphere. Weather varies by season and latitude. Ecosystems evolve over centuries.
+
+Earth-like worlds are the most familiar to players — moderate climate, diverse terrain, and
+balanced starting conditions. Most fictional homeworlds are built on this archetype.
+
+**Playing on an Earth-like world:** Balanced for all races and playstyles
+**Key features:** Weather events, ecological succession, river civilizations, fertile lowlands