fix: map the new exit code, keep add runnable, distinguish severity by shape

Copilot review round 4.

- Add `SCHEMA_UNPORTABLE` to `codeForExit`. `CliExitCodeError` lets a
  caller omit the envelope, so without the case an envelope-less throw
  reported the generic `error` — the same silent mislabelling the rename
  was meant to prevent, one layer down. Covered via the envelope-less
  construction that exposed it.

- Keep a local `type` (and the preset's `required`) alongside the remote
  `$ref` in the showcase config. The TUI's `schemaToForm` dispatches on
  `type`, so a `$ref`-only property fell through to a string field that
  `add`'s numeric handler then rejected — making the README's "every
  showcase tool is runnable" claim false there. The `remote-ref` finding
  is unaffected, since that rule reads `$ref` independently.

- Restrict `type-union` to well-formed unions: non-empty, unique, and
  all recognized JSON Schema type names. Its message asserts the
  construct is *legal* JSON Schema, which is false for `[]`, `[3]` or
  `["bananas"]`, and the `anyOf` it suggested for those would be invalid
  too. Malformed schemas stay the SDK parser's business.

- Drop `if`/`then`/`else` from the presence-only allowlist. They only
  constrain as a pair, so `{"if": {"const": 1}}` accepts every value and
  was evading `untyped-schema`; the pairing is now checked explicitly.

- Distinguish the web sidebar severities by SHAPE, not just colour — a
  circle for an error, a triangle for a warning — and name the severity
  in the tooltip. Colour alone left a colour-blind reader unable to tell
  them apart.

- Fix the stale "across 2 tools" count in the CLI README's hint sample.

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/tui/__tests__/schemaToForm.test.ts

@@ -381,5 +381,31 @@ describe("schemaToForm", () => {
         type: "string",
       });
     });
+
+    // #1005: the unportable-schemas showcase advertises a remote `$ref` so the
+    // lint has a `remote-ref` finding to report. A `$ref`-only property falls
+    // through to a string field here, which the tool's real (numeric) handler
+    // then rejects — so the fixture keeps a local `type` alongside the ref and
+    // the tool stays runnable. This pins the half of that contract the TUI
+    // owns; the wire half is in `raw-tool-schemas.test.ts`.
+    it("types a property that carries both a remote $ref and a local type", () => {
+      const form = schemaToForm(
+        {
+          properties: {
+            a: {
+              type: "number",
+              $ref: "https://example.com/schemas/number.json",
+            },
+          },
+        },
+        "refWithLocalType",
+      );
+      // `float` is this form builder's numeric field kind — the point is that
+      // it is NOT the string fallback a `$ref`-only property would get.
+      expect(form.sections[0]!.fields[0]).toMatchObject({
+        name: "a",
+        type: "float",
+      });
+    });
   });
 });