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.

src/daemonClient.ts

@@ -22,6 +22,7 @@ function unwrap(resp: DaemonResponse): unknown {
 // daemon injects textDocument.uri from `file`, so callers omit it.
 export async function daemonRequest(
   file: string,
+  serverId: string,
   method: string,
   params: Record<string, unknown>,
 ): Promise<unknown> {
@@ -29,6 +30,7 @@ export async function daemonRequest(
     await sendOnce({
       op: "request",
       file,
+      serverId,
       method,
       params,
       launch: buildLaunchContext(),
@@ -38,14 +40,18 @@ export async function daemonRequest(
 
 // Wait For Diagnostics - Diagnostics arrive as a notification, not a
 // response, so the daemon has a dedicated op that awaits the next publish.
+// Accepts an array of server IDs; daemon fans out in parallel and returns
+// a grouped map: { [serverId]: { uri, diagnostics[] } }.
 export async function daemonDiagnostics(
   file: string,
+  serverIds: string[],
   timeoutMs = 1500,
 ): Promise<unknown> {
   return unwrap(
     await sendOnce({
       op: "diagnostics",
       file,
+      serverIds,
       timeoutMs,
       launch: buildLaunchContext(),
     }),