fix: drop the unreachable root rule, correct the always-false suggestion

Copilot review round 2.

- Remove `non-object-root` entirely. It could never fire: the SDK types
  `inputSchema` with `type: literal("object")`, so a tool with any other
  root fails `ListToolsResultSchema` and `salvageListItems` drops it
  before any client sees it. Verified against a live server advertising
  `inputSchema: {type: "array"}` — `listAllTools()` returns []. A rule
  that cannot fire is worse than none, because the docs then claim a
  check the tool does not perform; the condition is already reported
  through the malformed-items surface. Pinned by an integration test so
  a change in that behavior is a signal rather than a silent gap.

- Fix the bare-`false` suggestion. `properties: {a: false}` forbids the
  property; deleting the entry *permits* it with any value under the
  default `additionalProperties`, so the advice inverted the schema it
  replaced. Now recommends `{"not": {}}` and says why deletion differs.

- Exempt `not`-parented schemas from `untyped-schema`, so the `{"not":
  {}}` above does not trip this module's own rule — under negation an
  always-accepting subschema means always-reject, making "accepts any
  value" the exact opposite of what it does. Scoped to that position,
  not inherited by its subtree.

- Say plainly, in the `true` and untyped suggestions, that they narrow
  the schema deliberately rather than implying an equivalent rewrite.
  `true` has no portable object-form equivalent — `{}` is the very shape
  this lint flags.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01UL9retfvAXRgvi6EWk4SY4
Signed-off-by: cliffhall <cliff@futurescale.com>

clients/web/src/test/integration/mcp/raw-tool-schemas.test.ts

@@ -110,6 +110,24 @@ describe("rawToolSchemas override (#1005)", () => {
     ]);
   });
 
+  it("drops a tool whose inputSchema root is not an object, before any client sees it", async () => {
+    // This is why `schemaLint` has no "inputSchema must be an object" rule.
+    // The SDK types `inputSchema` with `type: literal("object")`, so such a
+    // tool fails `ListToolsResultSchema` and `salvageListItems` removes it —
+    // no client can pass it to the lint, and a rule for it could never fire.
+    // If this ever starts returning the tool, that rule becomes worth adding
+    // back and this test is the signal.
+    const started = await start({
+      rawToolSchemas: {
+        echo: { inputSchema: { type: "array", items: { type: "string" } } },
+      },
+    });
+    const connected = await connect(started.url);
+
+    const { tools } = await connected.listAllTools();
+    expect(tools.map((t) => t.name)).toEqual(["get_weather"]);
+  });
+
   it("leaves an unnamed tool's real schema alone", async () => {
     const started = await start({
       rawToolSchemas: { echo: { outputSchema: { type: "object" } } },