feat: theme config service — REST API with versioning + backup

- ThemeService: read/write/validate theme.json, auto-backup on save
- ThemeController: GET/PUT/POST /api/config/theme (public GET, versioned PUT)
- ThemeConfig type with version + updatedAt fields
- Default theme: Global Hospital blue scale
- ConfigThemeModule registered in AppModule

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

src/config/theme.service.ts

@@ -0,0 +1,98 @@
+import { Injectable, Logger, OnModuleInit } from '@nestjs/common';
+import { readFileSync, writeFileSync, existsSync, mkdirSync, copyFileSync } from 'fs';
+import { join, dirname } from 'path';
+import { DEFAULT_THEME, type ThemeConfig } from './theme.defaults';
+
+const THEME_PATH = join(process.cwd(), 'data', 'theme.json');
+const BACKUP_DIR = join(process.cwd(), 'data', 'theme-backups');
+
+@Injectable()
+export class ThemeService implements OnModuleInit {
+    private readonly logger = new Logger(ThemeService.name);
+    private cached: ThemeConfig | null = null;
+
+    onModuleInit() {
+        this.load();
+    }
+
+    getTheme(): ThemeConfig {
+        if (this.cached) return this.cached;
+        return this.load();
+    }
+
+    updateTheme(updates: Partial<ThemeConfig>): ThemeConfig {
+        const current = this.getTheme();
+
+        const merged: ThemeConfig = {
+            brand: { ...current.brand, ...updates.brand },
+            colors: {
+                brand: { ...current.colors.brand, ...updates.colors?.brand },
+            },
+            typography: { ...current.typography, ...updates.typography },
+            login: { ...current.login, ...updates.login, poweredBy: { ...current.login.poweredBy, ...updates.login?.poweredBy } },
+            sidebar: { ...current.sidebar, ...updates.sidebar },
+            ai: {
+                quickActions: updates.ai?.quickActions ?? current.ai.quickActions,
+            },
+        };
+
+        merged.version = (current.version ?? 0) + 1;
+        merged.updatedAt = new Date().toISOString();
+
+        this.backup();
+
+        const dir = dirname(THEME_PATH);
+        if (!existsSync(dir)) mkdirSync(dir, { recursive: true });
+        writeFileSync(THEME_PATH, JSON.stringify(merged, null, 2), 'utf8');
+        this.cached = merged;
+
+        this.logger.log(`Theme updated to v${merged.version}`);
+        return merged;
+    }
+
+    resetTheme(): ThemeConfig {
+        this.backup();
+        const dir = dirname(THEME_PATH);
+        if (!existsSync(dir)) mkdirSync(dir, { recursive: true });
+        writeFileSync(THEME_PATH, JSON.stringify(DEFAULT_THEME, null, 2), 'utf8');
+        this.cached = DEFAULT_THEME;
+        this.logger.log('Theme reset to defaults');
+        return DEFAULT_THEME;
+    }
+
+    private load(): ThemeConfig {
+        try {
+            if (existsSync(THEME_PATH)) {
+                const raw = readFileSync(THEME_PATH, 'utf8');
+                const parsed = JSON.parse(raw);
+                this.cached = {
+                    brand: { ...DEFAULT_THEME.brand, ...parsed.brand },
+                    colors: { brand: { ...DEFAULT_THEME.colors.brand, ...parsed.colors?.brand } },
+                    typography: { ...DEFAULT_THEME.typography, ...parsed.typography },
+                    login: { ...DEFAULT_THEME.login, ...parsed.login, poweredBy: { ...DEFAULT_THEME.login.poweredBy, ...parsed.login?.poweredBy } },
+                    sidebar: { ...DEFAULT_THEME.sidebar, ...parsed.sidebar },
+                    ai: { quickActions: parsed.ai?.quickActions ?? DEFAULT_THEME.ai.quickActions },
+                };
+                this.logger.log('Theme loaded from file');
+                return this.cached;
+            }
+        } catch (err) {
+            this.logger.warn(`Failed to load theme: ${err}`);
+        }
+
+        this.cached = DEFAULT_THEME;
+        this.logger.log('Using default theme');
+        return DEFAULT_THEME;
+    }
+
+    private backup() {
+        try {
+            if (!existsSync(THEME_PATH)) return;
+            if (!existsSync(BACKUP_DIR)) mkdirSync(BACKUP_DIR, { recursive: true });
+            const ts = new Date().toISOString().replace(/[:.]/g, '-');
+            copyFileSync(THEME_PATH, join(BACKUP_DIR, `theme-${ts}.json`));
+        } catch (err) {
+            this.logger.warn(`Backup failed: ${err}`);
+        }
+    }
+}