feat: single-source cross-app wire contracts in @boocode/contracts (v2.7.13)

Move all hand-synced cross-app wire contracts into one built workspace
package, @boocode/contracts, consumed by server/web/coder/coder-web via
workspace:* + a per-subpath exports map. The ws-frames and provider-config
Zod schemas are schema-first (z.infer); MessageMetadata, ErrorReason,
AgentSessionConfig, the provider snapshot types, and WorktreeRiskReport are
each single-sourced. Deletes the byte-identical copies and their parity
tests, fixes a live AgentSessionConfig drift (coder dead copy removed,
unified to the web required/nullable shape), removes the dead pending_change
WS arms in the fallback SPA, and inverts the build order (contracts builds
first) across root build, Dockerfile, and the coder deploy docs. Reverses
the shared-package decision declined in v2.5.12.

apps/coder/web/src/pages/Session.tsx

@@ -14,8 +14,7 @@ export function Session() {
   const [chat, setChat] = useState<Chat | null>(null);
   const [loading, setLoading] = useState(true);
 
-  const { messages, connected, isStreaming, onPendingChange } =
-    useSessionStream(sessionId);
+  const { messages, connected, isStreaming } = useSessionStream(sessionId);
 
   // Get or create a chat for this session
   useEffect(() => {
@@ -78,9 +77,7 @@ export function Session() {
           connected={connected}
         />
       }
-      diffPane={
-        <DiffPane sessionId={sessionId} onPendingChange={onPendingChange} />
-      }
+      diffPane={<DiffPane sessionId={sessionId} />}
     />
   );
 }