feat(mosaic): add top-level mosaic config command (CU-04-04, CU-04-05)

Adds `mosaic config` command tree with five subcommands (show, get, set,
edit, path) backed by ConfigService; adds minimal get/set/path/readAll
primitives to ConfigService + FileConfigAdapter. Includes Vitest tests.

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

packages/mosaic/src/config/file-adapter.ts

@@ -1,6 +1,6 @@
 import { readFileSync, existsSync, readdirSync, statSync, copyFileSync } from 'node:fs';
 import { join } from 'node:path';
-import type { ConfigService } from './config-service.js';
+import type { ConfigService, ConfigSection, ResolvedConfig } from './config-service.js';
 import type { SoulConfig, UserConfig, ToolsConfig, InstallAction } from '../types.js';
 import { soulSchema, userSchema, toolsSchema } from './schemas.js';
 import { renderTemplate } from '../template/engine.js';
@@ -159,6 +159,73 @@ export class FileConfigAdapter implements ConfigService {
     }
   }
 
+  async readAll(): Promise<ResolvedConfig> {
+    const [soul, user, tools] = await Promise.all([
+      this.readSoul(),
+      this.readUser(),
+      this.readTools(),
+    ]);
+    return { soul, user, tools };
+  }
+
+  async getValue(dottedKey: string): Promise<unknown> {
+    const parts = dottedKey.split('.');
+    const section = parts[0] ?? '';
+    const field = parts.slice(1).join('.');
+    const config = await this.readAll();
+    if (!this.isValidSection(section)) return undefined;
+    const sectionData = config[section as ConfigSection] as Record<string, unknown>;
+    return field ? sectionData[field] : sectionData;
+  }
+
+  async setValue(dottedKey: string, value: string): Promise<unknown> {
+    const parts = dottedKey.split('.');
+    const section = parts[0] ?? '';
+    const field = parts.slice(1).join('.');
+    if (!this.isValidSection(section) || !field) {
+      throw new Error(
+        `Invalid key "${dottedKey}". Use format <section>.<field> (e.g. soul.agentName).`,
+      );
+    }
+
+    const previous = await this.getValue(dottedKey);
+
+    if (section === 'soul') {
+      const current = await this.readSoul();
+      await this.writeSoul({ ...current, [field]: value });
+    } else if (section === 'user') {
+      const current = await this.readUser();
+      await this.writeUser({ ...current, [field]: value });
+    } else {
+      const current = await this.readTools();
+      await this.writeTools({ ...current, [field]: value });
+    }
+
+    return previous;
+  }
+
+  getConfigPath(section?: ConfigSection): string {
+    if (!section) return this.mosaicHome;
+    const fileMap: Record<ConfigSection, string> = {
+      soul: join(this.mosaicHome, 'SOUL.md'),
+      user: join(this.mosaicHome, 'USER.md'),
+      tools: join(this.mosaicHome, 'TOOLS.md'),
+    };
+    return fileMap[section];
+  }
+
+  isInitialized(): boolean {
+    return (
+      existsSync(join(this.mosaicHome, 'SOUL.md')) ||
+      existsSync(join(this.mosaicHome, 'USER.md')) ||
+      existsSync(join(this.mosaicHome, 'TOOLS.md'))
+    );
+  }
+
+  private isValidSection(s: string): s is ConfigSection {
+    return s === 'soul' || s === 'user' || s === 'tools';
+  }
+
   /**
    * Look for template in source dir first, then mosaic home.
    */