refactor(schema): rename biome_summary to planet_class (D-188)

"Biome" describes per-zone vegetation classification (Whittaker table).
"Planet class" describes overall planetary character. The conflation
caused the planet generator to misclassify ~270 bodies as barren.

Scope: systems.db column, schema SQL, Rust atlas code, wiki table
headers (Biome → Class), atlas proposal JSONs, all docs/decisions,
tooling scripts. Also normalizes atmosphere vocabulary (breathable →
standard) and expands planet class mapping to all 26 wiki values.
Unknown classes default to temperate for modder safety.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

server/src/bin/atlas/sync_wiki.rs

@@ -35,7 +35,7 @@ pub fn cmd_sync_wiki(conn: &Connection, system_id: Option<&str>, wiki_dir: &str)
                 "SELECT body_id, proper_name, body_type, orbit_index, parent_body_id,
                         inhabited, population, mass_class, atmosphere, surface_gravity,
                         orbital_period_days, rotation_period_hours,
-                        biome_summary, hydrosphere, economic_role, settlement_pattern,
+                        planet_class, hydrosphere, economic_role, settlement_pattern,
                         industrial_corridor
                  FROM bodies WHERE system_id = ?1
                  ORDER BY CASE WHEN parent_body_id IS NULL THEN orbit_index ELSE 1000 + orbit_index END",