Add generative panels, provider settings UI, and credits

Frontend:
- tools/ai_replace_selection.js: use any selection → remote inpaint with prompt
- modules/generate/text_to_image.js: Text → Image dialog (new layer or replace canvas)
- modules/generate/outpaint.js: Expand Canvas in any direction via remote provider
- modules/tools/ai_provider_settings.js: in-app provider config (OpenAI / InvokeAI /
  ComfyUI / Replicate); persists to localStorage, pushes to POST /api/config at runtime
- config.js: register ai_replace_selection tool
- config-menu.js: add Generate menu (Text→Image, Outpaint); AI Provider Settings under Tools
- modules/help/about.js: updated credits (LaMa, rembg, SAM, InvokeAI, ComfyUI, OpenAI)
- api/capabilities.js: add refreshCapabilities() for post-save cache invalidation

Backend:
- routers/ai_tools.py: POST /api/config — apply provider settings at runtime
  without restart (session-scoped, non-persistent; .env for permanence)

https://claude.ai/code/session_01B58MaJCU1R6KwBDJCp8AfN

frontend/src/js/api/capabilities.js

@@ -48,9 +48,18 @@ export function hasRemote() {
     return !!(_caps?.remote?.healthy);
 }
 
+/**
+ * Invalidate cache and re-fetch (call after saving provider settings).
+ */
+export async function refreshCapabilities() {
+    _caps = null;
+    _fetchPromise = null;
+    return getCapabilities();
+}
+
 /**
  * Kick off the fetch immediately at module load time so it's ready when tools need it.
  */
 getCapabilities();
 
-export default { getCapabilities, getCachedCapabilities, hasRemote };
+export default { getCapabilities, getCachedCapabilities, hasRemote, refreshCapabilities };