Real per-step progress bars for local GPU inference

Backend:
- local_diffusion.py: add _make_step_cb() that writes step/total_steps/
  progress into _states on every diffusers callback_on_step_end; wired into
  txt2img, inpaint, img2img with TypeError fallback for older diffusers
- ai_tools.py: GET /api/generate/progress SSE endpoint — streams _states
  as JSON array every 200ms so clients get live denoising step counts

Frontend:
- progress_overlay.js: add connectProgressSSE(pipeType, baseUrl) /
  disconnectProgressSSE() — opens EventSource, maps step/total_steps
  to bar percentage (0→85% during denoising, 85→100 for decode/place)
- text_to_image.js: connect SSE before POST, disconnect on done/error
- selection_actions.js: connect SSE for AI edit / asymmetry operations

Result: for local GPU, progress bar shows "Step 12 / 30" with exact fill;
for remote providers and upscale (no step callbacks), shimmer animates.

https://claude.ai/code/session_01WVDg7amsy1TTtxvpku7bcM

frontend/src/js/tools/selection_actions.js

@@ -18,7 +18,7 @@ import app from './../app.js';
 import config from './../config.js';
 import Base_layers_class from './../core/base-layers.js';
 import alertify from './../../../node_modules/alertifyjs/build/alertify.min.js';
-import { showProgress, hideProgress } from './../libs/progress_overlay.js';
+import { showProgress, updateProgress, hideProgress, connectProgressSSE, disconnectProgressSSE } from './../libs/progress_overlay.js';
 
 const BASE = window.API_BASE_URL || '';
 
@@ -196,6 +196,7 @@ export class SelectionActions {
     async _makeAsymmetric() {
         if (!this._check()) return;
         this.hide();
+        connectProgressSSE('inpaint', window.API_BASE_URL || '');
         showProgress('AI is adding natural asymmetry…', 60);
         try {
             var res = await _post('/api/image/ai-edit-region', {
@@ -208,9 +209,11 @@ export class SelectionActions {
             });
             this.tool.updateLayerWithResult(res.result);
             this.tool.clearSelection();
+            disconnectProgressSSE();
             hideProgress();
             alertify.success('Made less symmetrical!');
         } catch (e) {
+            disconnectProgressSSE();
             hideProgress();
             alertify.error('AI edit failed: ' + e.message);
         }
@@ -219,6 +222,7 @@ export class SelectionActions {
     async _aiEditRegion(instruction) {
         if (!this._check()) return;
         this.hide();
+        connectProgressSSE('inpaint', window.API_BASE_URL || '');
         showProgress('AI is editing the region…', 60);
         try {
             var res = await _post('/api/image/ai-edit-region', {
@@ -230,9 +234,11 @@ export class SelectionActions {
             });
             this.tool.updateLayerWithResult(res.result);
             this.tool.clearSelection();
+            disconnectProgressSSE();
             hideProgress();
             alertify.success('Done!');
         } catch (e) {
+            disconnectProgressSSE();
             hideProgress();
             alertify.error('AI edit failed: ' + e.message);
         }