refactor: rename atlas agent to Atlas for naming consistency

- Rename agent name from 'atlas' to 'Atlas' (PascalCase like Sisyphus, Metis, Momus)
- Add migration for lowercase 'atlas' -> 'Atlas' for backward compatibility
- Keep hook name as 'atlas' (lowercase) to match other hook naming conventions
- Update all references in types, schema, hooks, commands, and tests

src/config/schema.ts

@@ -24,7 +24,7 @@ export const BuiltinAgentNameSchema = z.enum([
   "multimodal-looker",
   "Metis (Plan Consultant)",
   "Momus (Plan Reviewer)",
-  "atlas",
+  "Atlas",
 ])
 
 export const BuiltinSkillNameSchema = z.enum([
@@ -46,7 +46,7 @@ export const OverridableAgentNameSchema = z.enum([
   "librarian",
   "explore",
   "multimodal-looker",
-  "atlas",
+  "Atlas",
 ])
 
 export const AgentNameSchema = BuiltinAgentNameSchema
@@ -127,7 +127,7 @@ export const AgentOverridesSchema = z.object({
   librarian: AgentOverrideConfigSchema.optional(),
   explore: AgentOverrideConfigSchema.optional(),
   "multimodal-looker": AgentOverrideConfigSchema.optional(),
-  atlas: AgentOverrideConfigSchema.optional(),
+  Atlas: AgentOverrideConfigSchema.optional(),
 })
 
 export const ClaudeCodeConfigSchema = z.object({