refactor(daemon): require explicit serverId on all daemon ops

Move all server matching logic to the extension/CLI side. The daemon no
longer calls pickServer() — it receives an explicit serverId (or
serverIds[] for diagnostics) and uses it directly for cache lookup and
server spawning.

Key changes:
- request op requires serverId: string
- diagnostics op requires serverIds: string[] — daemon fans out in
  parallel via Promise.allSettled and returns grouped map
- formatDiagnostics() handles grouped results with per-server headers
  when multiple servers contribute (single-server omits header)
- CLI picks servers locally before calling daemon helpers
- New pickDiagnosticServers() in extension returns all available,
  non-disabled servers matching the file extension

This makes multi-server diagnostics (e.g., typescript-language-server +
oxlint) work naturally — the extension decides which servers to query,
the daemon just executes.

cli.ts

@@ -2,7 +2,8 @@
 import * as path from "node:path";
 import { startClientForFile } from "./src/client.ts";
 import { isLspCommand, listCommands, runCommand } from "./src/commands.ts";
-import { pickServer } from "./src/root.ts";
+import { pickServer, isServerAvailable } from "./src/root.ts";
+import { servers } from "./server.ts";
 import {
   daemonDiagnostics,
   daemonRequest,
@@ -104,14 +105,20 @@ async function runViaDaemon(
   const filePath = path.resolve(fileArg);
   let result: unknown;
   if (cmdArg === "diagnostics") {
-    result = await daemonDiagnostics(filePath);
+    // Pick All Available Servers For Diagnostics
+    const ext = path.extname(filePath).replace(/^\./, "");
+    const serverIds = servers
+      .filter((s) => s.match.includes(ext) && isServerAvailable(s))
+      .map((s) => s.id);
+    result = await daemonDiagnostics(filePath, serverIds);
   } else if (cmdArg in methodMap) {
+    const server = pickServer(filePath);
     // References Default - Match commands.ts: include declaration unless
     // caller explicitly overrode `context`.
     if (cmdArg === "references" && !("context" in params)) {
       params.context = { includeDeclaration: true };
     }
-    result = await daemonRequest(filePath, methodMap[cmdArg], params);
+    result = await daemonRequest(filePath, server.id, methodMap[cmdArg], params);
   } else {
     process.stderr.write(
       `Unknown command "${cmdArg}". Known: ${listCommands().join(", ")}\n`,