Improve ACPX adapter configuration (#5290)

## Thinking Path

> - Paperclip orchestrates AI agents across several adapter
implementations.
> - ACPX is a local adapter path that can proxy Claude and Codex-style
execution.
> - Its configuration needed stronger schema defaults, provider-aware
model handling, and better UI support.
> - Plugin authors also need clear docs for managed resources.
> - This pull request improves ACPX adapter configuration and documents
plugin-managed resources.
> - The benefit is a more predictable adapter setup path without
changing unrelated control-plane behavior.

## What Changed

- Improved ACPX config schema, execution config handling, UI build
config, and route coverage.
- Added ACPX model filtering support and tests.
- Updated the agent config form and storybook coverage for ACPX
model/provider behavior.
- Expanded plugin authoring documentation for managed resources.

## Verification

- `pnpm install --frozen-lockfile`
- `pnpm exec vitest run server/src/__tests__/acpx-local-execute.test.ts
server/src/__tests__/adapter-routes.test.ts
ui/src/lib/acpx-model-filter.test.ts`

## Risks

- Low-to-medium risk: adapter configuration behavior changes can affect
ACPX users, but the change is isolated to ACPX/plugin-doc surfaces and
covered by targeted adapter tests.

## Model Used

- OpenAI GPT-5 Codex via Paperclip `codex_local` adapter, with
shell/git/GitHub CLI tool use.

## Checklist

- [x] I have included a thinking path that traces from project context
to this change
- [x] I have specified the model used (with version and capability
details)
- [x] I have checked ROADMAP.md and confirmed this PR does not duplicate
planned core work
- [x] I have run tests locally and they pass
- [x] I have added or updated tests where applicable
- [x] If this change affects the UI, I have included before/after
screenshots
- [x] I have updated relevant documentation to reflect my changes
- [x] I have considered and documented any risks above
- [x] I will address all Greptile and reviewer comments before
requesting merge

---------

Co-authored-by: Paperclip <noreply@paperclip.ing>

server/src/__tests__/adapter-routes.test.ts

@@ -248,11 +248,33 @@ describe("adapter routes", () => {
           ]),
         }),
         expect.objectContaining({
-          key: "permissionMode",
-          default: "approve-all",
+          key: "fastMode",
+          default: false,
+          meta: { visibleWhen: { key: "agent", values: ["codex"] } },
+        }),
+        expect.objectContaining({
+          key: "warmHandleIdleMs",
+          default: 0,
         }),
       ]),
     );
+    const keys = res.body.fields.map((field: { key: string }) => field.key);
+    expect(keys).not.toContain("mode");
+    expect(keys).not.toContain("permissionMode");
+    expect(keys).not.toContain("instructionsFilePath");
+    expect(keys).not.toContain("promptTemplate");
+    expect(keys).not.toContain("bootstrapPromptTemplate");
+  });
+
+  it("GET /api/adapters includes ACPX model availability", async () => {
+    const app = createApp();
+
+    const res = await request(app).get("/api/adapters");
+
+    expect(res.status, JSON.stringify(res.body)).toBe(200);
+    const acpxLocal = res.body.find((a: any) => a.type === "acpx_local");
+    expect(acpxLocal).toBeDefined();
+    expect(acpxLocal.modelsCount).toBeGreaterThan(0);
   });
 
   it("rejects signed-in users without org access", async () => {