feat: allow complex JSON values in request _meta

Closes #1910

`_meta` was typed `Record<string, string>` end to end in the Inspector —
on disk as a `{ key, value }[]` pair array, in the Server Settings form as
key/value rows, and in every request verb's per-call metadata parameter.
Nothing in the MCP spec restricts a `_meta` value to a string, and the SDK
models the field as a `z.looseObject`, so the restriction was ours alone.

Widen the whole path to `RequestMetadata` (`Record<string, JsonValue>`):

- Per-server default metadata is a JSON **object** on disk and in memory.
  The pre-#1910 pair array is still read (`normalizeStoredMetadata`) so an
  existing `mcp.json` keeps working; it is never written back, so a save
  migrates the entry.
- The Server Settings → Request Metadata section is a JSON editor
  (`JsonObjectInput`) instead of key/value rows — rows cannot express an
  object value. It keeps the typed text as the display source and emits
  only parsed JSON, the same draft split `SchemaJsonField` uses, so the box
  stays typeable; invalid text is flagged inline and not applied.
- The CLI stops flattening `--metadata` / `--tool-metadata` through
  `metaValueToString`. Those values were already JSON-parsed, so
  `trace={"id":"abc"}` used to reach the wire as the *string* `{"id":"abc"}`
  and now reaches it as an object.
- `servers/show` redaction replaces a sensitive key's whole value rather
  than a string, so a structured value cannot leak through its members.
- `progressTokenOf` narrows the reserved `progressToken` key back to
  `string | number` before it reaches the SDK; any other JSON still travels
  inside `_meta` but wires up no progress callback.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_0177mPHAdECD18nLLCTwR5rh
Signed-off-by: cliffhall <cliff@futurescale.com>

clients/web/src/components/groups/ServerSettingsModal/ServerSettingsModal.tsx

@@ -5,6 +5,7 @@ import type {
   InspectorServerSettings,
   ModernLogLevel,
   OAuthSettings,
+  RequestMetadata,
   ServerProtocolEra,
   ServerType,
 } from "@inspector/core/mcp/types.js";
@@ -155,24 +156,7 @@ export function ServerSettingsModal({
     onSettingsChange({ ...settings, cwd: value });
   }
 
-  function handleAddMetadata() {
-    onSettingsChange({
-      ...settings,
-      metadata: [...settings.metadata, { key: "", value: "" }],
-    });
-  }
-
-  function handleRemoveMetadata(index: number) {
-    onSettingsChange({
-      ...settings,
-      metadata: settings.metadata.filter((_, i) => i !== index),
-    });
-  }
-
-  function handleMetadataChange(index: number, key: string, value: string) {
-    const metadata = settings.metadata.map((m, i) =>
-      i === index ? { key, value } : m,
-    );
+  function handleMetadataChange(metadata: RequestMetadata) {
     onSettingsChange({ ...settings, metadata });
   }
 
@@ -303,8 +287,6 @@ export function ServerSettingsModal({
             onRemoveEnv={handleRemoveEnv}
             onEnvChange={handleEnvChange}
             onCwdChange={handleCwdChange}
-            onAddMetadata={handleAddMetadata}
-            onRemoveMetadata={handleRemoveMetadata}
             onMetadataChange={handleMetadataChange}
             onTimeoutChange={handleTimeoutChange}
             onAutoRefreshChange={handleAutoRefreshChange}