fix image stale-render on in-place overwrite (T-312)

Image cards, thumbnails, the lightbox, and `clide image show` rendered
via Image.file, whose FileImage keys Flutter's imageCache by (path,
scale) only — so overwriting a file at the same path handed back the
previously decoded frame (hit live re-exporting a wireframe PNG). Add
ClideFileImage, a FileImage that folds mtime + size into ==/hashCode so an
in-place change is a fresh cache key (miss → re-decode), and route the
five Image.file sites through it.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

lib/builtin/claude/src/conversation_view.dart

@@ -11,7 +11,6 @@ library;
 
 import 'dart:async';
 import 'dart:convert';
-import 'dart:io';
 
 import 'package:clide/builtin/claude/src/activity_cluster.dart';
 import 'package:clide/builtin/claude/src/conversation_card.dart';
@@ -499,8 +498,8 @@ class _ConversationTurn extends StatelessWidget {
                 borderRadius: BorderRadius.circular(4),
                 child: ConstrainedBox(
                   constraints: const BoxConstraints(maxHeight: 360),
-                  child: Image.file(
-                    File(m.path),
+                  child: Image(
+                    image: ClideFileImage(m.path),
                     fit: BoxFit.contain,
                     alignment: Alignment.centerLeft,
                     errorBuilder: (_, __, ___) => _imagePlaceholder(m.path),
@@ -522,8 +521,8 @@ class _ConversationTurn extends StatelessWidget {
     ClideKernel.of(context).dialog.show<Object>(
           (ctx, dismiss) => ClideLightbox(
             onDismiss: dismiss,
-            child: Image.file(
-              File(path),
+            child: Image(
+              image: ClideFileImage(path),
               fit: BoxFit.contain,
               errorBuilder: (_, __, ___) => _imagePlaceholder(path),
             ),

lib/builtin/claude/src/extension.dart

@@ -378,7 +378,7 @@ class ClaudeExtension extends ClideExtension {
       _ctx?.dialog.show<Object>(
         (c, dismiss) => ClideLightbox(
           onDismiss: dismiss,
-          child: Image.file(File(path), fit: BoxFit.contain),
+          child: Image(image: ClideFileImage(path), fit: BoxFit.contain),
         ),
       );
       return;

lib/builtin/claude/src/image_thumbnail.dart

@@ -3,14 +3,13 @@
 /// A bounded, keyboard-activatable thumbnail that opens the full image in the
 /// shared lightbox (T-252) on tap. Used both for `@<path>` image tokens in the
 /// conversation log and for the composer's attachment chips, so the two stay
-/// visually consistent. Reads the file directly via `Image.file` (dart:io) —
-/// pasted temp files live outside the workspace, so this is not gated by the
-/// `files.read` allow-list (D-80); it's display-only. A missing/unreadable file
-/// degrades to a muted placeholder instead of throwing.
+/// visually consistent. Reads the file directly via [ClideFileImage] (which
+/// re-decodes when the file changes in place, T-312) — pasted temp files live
+/// outside the workspace, so this is not gated by the `files.read` allow-list
+/// (D-80); it's display-only. A missing/unreadable file degrades to a muted
+/// placeholder instead of throwing.
 library;
 
-import 'dart:io';
-
 import 'package:clide/kernel/kernel.dart';
 import 'package:clide/widgets/widgets.dart';
 import 'package:flutter/widgets.dart';
@@ -20,8 +19,8 @@ void openImageLightbox(BuildContext context, String path) {
   ClideKernel.of(context).dialog.show<Object>(
         (ctx, dismiss) => ClideLightbox(
           onDismiss: dismiss,
-          child: Image.file(
-            File(path),
+          child: Image(
+            image: ClideFileImage(path),
             fit: BoxFit.contain,
             errorBuilder: (ctx, _, __) => _placeholder(ctx, 48),
           ),
@@ -65,8 +64,8 @@ class ImageThumbnail extends StatelessWidget {
           ),
           child: ClipRRect(
             borderRadius: BorderRadius.circular(radius),
-            child: Image.file(
-              File(path),
+            child: Image(
+              image: ClideFileImage(path),
               width: size,
               height: size,
               fit: BoxFit.cover,