Add LaMa magic eraser, remote provider abstraction, and AI tool infrastructure

Backend:
- requirements.txt: add simple-lama-inpainting, rembg[gpu]; upgrade opencv to 4.10+
- app/config.py: add InvokeAI (url, model) and ComfyUI (url, model) settings; OPENAI_MODEL
- app/services/local_inpaint.py: LaMa, OpenCV, rembg wrappers (auto GPU/CPU)
- app/services/remote_provider.py: abstract RemoteAIProvider + OpenAI, InvokeAI, ComfyUI drivers
- app/routers/ai_tools.py: new /api/* endpoints — /erase, /inpaint/lama, /inpaint/fast,
  /background/remove, /inpaint/remote, /generate/txt2img, /generate/img2img,
  /generate/outpaint, GET /config (capability flags)
- app/main.py: register ai_tools router

Frontend:
- services/api.js: add erase(), textToImage(), imageToImage(), remoteInpaint(), getConfig()
- api/capabilities.js: lazy-fetch /api/config singleton; hasRemote() helper
- tools/ai_lama_erase.js: brush-paint mask → LaMa erase → apply to layer
- tools/ai_smart_inpaint.js: brush mask + dialog (Fast/Quality mode + prompt) → inpaint
- core/components/provider-badge.js: shows active provider + health in toolbar
- config.js: register ai_lama_erase and ai_smart_inpaint tools
- main.js: mount provider badge on load
- .env.example: document InvokeAI, ComfyUI, OpenAI provider settings

https://claude.ai/code/session_01B58MaJCU1R6KwBDJCp8AfN

frontend/src/js/api/capabilities.js

@@ -0,0 +1,56 @@
+/**
+ * Backend capabilities singleton.
+ * Fetched once on load from GET /api/config.
+ * Tools use this to decide whether to show, grey out, or show tooltips.
+ *
+ * Shape:
+ * {
+ *   local:  { lama, rembg, opencv, gpu_detected },
+ *   remote: { provider, capabilities: string[], healthy }
+ * }
+ */
+
+import apiService from '../services/api.js';
+
+const DEFAULT_CAPS = {
+    local:  { lama: false, rembg: false, opencv: true, gpu_detected: false },
+    remote: { provider: null, capabilities: [], healthy: false },
+};
+
+let _caps = null;
+let _fetchPromise = null;
+
+/**
+ * Return capabilities (fetched lazily, cached thereafter).
+ * Always resolves — falls back to DEFAULT_CAPS on network error.
+ */
+export async function getCapabilities() {
+    if (_caps) return _caps;
+    if (!_fetchPromise) {
+        _fetchPromise = apiService.getConfig()
+            .then(data => { _caps = data || DEFAULT_CAPS; return _caps; })
+            .catch(() => { _caps = DEFAULT_CAPS; return _caps; });
+    }
+    return _fetchPromise;
+}
+
+/**
+ * Synchronous check — returns cached value or DEFAULT_CAPS if not yet loaded.
+ */
+export function getCachedCapabilities() {
+    return _caps || DEFAULT_CAPS;
+}
+
+/**
+ * True if the remote provider is configured and healthy.
+ */
+export function hasRemote() {
+    return !!(_caps?.remote?.healthy);
+}
+
+/**
+ * Kick off the fetch immediately at module load time so it's ready when tools need it.
+ */
+getCapabilities();
+
+export default { getCapabilities, getCachedCapabilities, hasRemote };