feat: edit/revert sent messages via server revert API — Closes #56 (#80)

* feat: edit/revert sent messages via server revert API

Wires the mobile client up to the opencode server's session.revert /
session.unrevert endpoints (the same primitive the desktop TUI uses to
edit the last message). Long-press a user message bubble -> "Edit
message" reverts it server-side and prefills the composer with its
text; a banner offers Undo while the revert is pending (it's only
cleaned up server-side on the next prompt). Degrades gracefully with
an alert on older servers that 404 the /revert route.

Closes #56

* fix(revert): address code review findings on edit/revert message flow

- Confirm before overwriting an in-progress composer draft when editing
  a sent message (F2)
- Restore reverted message's file attachments into the composer, not
  just its text (F3)
- Distinguish 401/403 from other revert failures with an accurate
  "Authentication failed" message instead of a generic one (F4)
- Exclude optimistic "temp-" message IDs from the revert cutoff
  comparison so concurrently-sent messages aren't hidden (F9)

---------

Co-authored-by: engineer <engineer@gray-knight-m1.local>

src/components/chat/MessageBubble.tsx

@@ -16,12 +16,16 @@ interface Props {
   message: Message
   parts: Part[]
   isDark: boolean
+  // Only wired up for user messages — long-press opens the "Edit message" /
+  // revert action sheet. Identified by messageID (not a closure over parts)
+  // so it stays correct even if the memo below bails on a stale render.
+  onLongPress?: (messageID: string) => void
 }
 
 // TODO: Replace with streamdown-rn once React 19 types PR lands - it has
 // built-in block-level memoization that eliminates re-renders for stable blocks
 export const MessageBubble = memo(
-  function MessageBubble({ message, parts, isDark }: Props) {
+  function MessageBubble({ message, parts, isDark, onLongPress }: Props) {
     const isUser = message.role === "user"
 
     const textParts = parts.filter((p) => p.type === "text")
@@ -32,7 +36,10 @@ export const MessageBubble = memo(
     const reasoning = reasoningParts.map((p) => p.text).join("\n") || ""
 
     return (
-      <View
+      <TouchableOpacity
+        activeOpacity={isUser && onLongPress ? 0.7 : 1}
+        onLongPress={isUser && onLongPress ? () => onLongPress(message.id) : undefined}
+        disabled={!isUser || !onLongPress}
         style={[
           s.bubble,
           isUser ? s.user : s.assistant,
@@ -101,7 +108,7 @@ export const MessageBubble = memo(
             {message.cost ? ` · $${message.cost.toFixed(4)}` : ""}
           </Text>
         )}
-      </View>
+      </TouchableOpacity>
     )
   },
   (prev, next) => {
@@ -109,6 +116,7 @@ export const MessageBubble = memo(
     // This prevents completed messages from re-rendering during streaming
     if (prev.message.id !== next.message.id) return false
     if (prev.isDark !== next.isDark) return false
+    if (prev.onLongPress !== next.onLongPress) return false
     if (prev.parts.length !== next.parts.length) return false
     // Compare the last part's text content - this is what changes during streaming
     const prevLast = prev.parts[prev.parts.length - 1]