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/common.rs

@@ -19,7 +19,7 @@ pub struct BodyRow {
     pub mass_class: Option<String>,
     pub atmosphere: Option<String>,
     pub surface_gravity: Option<f64>,
-    pub biome_summary: Option<String>,
+    pub planet_class: Option<String>,
     pub hydrosphere: Option<String>,
     pub inhabited: bool,
     pub population: i64,
@@ -102,7 +102,7 @@ pub fn query_bodies(
     let mut sql = String::from(
         "SELECT body_id, system_id, parent_body_id, body_type, orbit_index,
                 proper_name, mass_class, atmosphere, surface_gravity,
-                biome_summary, hydrosphere, inhabited, population,
+                planet_class, hydrosphere, inhabited, population,
                 economic_role, cultural_corridor, industrial_corridor
          FROM bodies WHERE 1=1",
     );
@@ -138,7 +138,7 @@ pub fn query_bodies(
             mass_class: row.get(6)?,
             atmosphere: row.get(7)?,
             surface_gravity: row.get(8)?,
-            biome_summary: row.get(9)?,
+            planet_class: row.get(9)?,
             hydrosphere: row.get(10)?,
             inhabited: row.get::<_, i32>(11)? != 0,
             population: row.get::<_, Option<i64>>(12)?.unwrap_or(0),