feat(agent-presets): rename the two-tool preset to minimal

`core-web` said neither of the things that matter about it. The `-web`
suffix is a leftover from the whole-process `core-web.cordis.yml` overlay,
and presets are per-session and not web-specific. `core` reads as "the
foundational one" when it is in fact the one with the fewest capabilities.

`minimal` says what it is and orders the shipped set legibly by capability:
minimal, standard, cordis.

Breaking: a session created under `core-web` records that id in its header
and will fail to resolve it on resume. Nothing outside this repository has
shipped, so no migration path is offered.

The identically named `config/core-web.cordis.yml` — the legacy
whole-process overlay behind the web snapshot test — is a different thing
and keeps its name.

packages/client/connection/src/client/fixture.ts

@@ -1346,7 +1346,7 @@ export function createFixtureApi(options: FixtureOptions = {}): ApiProxy {
    */
   const fixturePresets = new Map<string, { trust: 'system' | 'user'; content: string }>([
     ['standard', { trust: 'system', content: "- id: tool-bash\n  name: '@deepseek-ai/dsh-tool-bash'\n" }],
-    ['core-web', { trust: 'system', content: "- id: tool-web-search\n  name: '@deepseek-ai/dsh-tool-web-search'\n" }],
+    ['minimal', { trust: 'system', content: "- id: tool-web-search\n  name: '@deepseek-ai/dsh-tool-web-search'\n" }],
     ['my-agent', { trust: 'user', content: "- id: tool-read\n  name: '@deepseek-ai/dsh-tool-read'\n" }],
   ])
   let fixtureDefaultPreset = 'standard'