fix(web): correct the preset-layer contracts review found stale

None of these change behavior; each said something that was not true.

`SessionCwdConflict`'s doc block had been left stranded above the
`AgentPresetConflict` inserted under it, so one class carried a comment
about the other and the second carried none.

The roster comment named a `.system` directory that does not exist; the
shipped root is `config/agent-presets/`, and `system` is the trust its
entries carry.

The real-composition test attributed the disabled `api-gateway` row to
"side effects outside this process" alongside the port and the exporter.
It is disabled for a different reason — the api-proxy cannot mount in
this layer at all — and hiding that behind the same phrase would leave a
later layer unable to tell whether the line can come out.

One test claimed to refuse an adoption while asserting only that the
header records the preset; it now says what it checks.

`PERSONA_SECTION`/`PERSONA_ORDER` existed twice, once in the registry
that declares the slot and once restated in the row that replaces it —
a drift that would land a preset's persona beside the deployment's
instead of shadowing it. The registry exports them now.

The preset conflict message read "already runs agent preset undefined"
for a session that records none, which is the shape a deployment with no
roster produces; it names that case instead, with the regression that
reaches it through the gateway.

Finally, `PresetTree.write()` drops the `loader/config-update` the
inherited method emits — recorded on the override, since a future
edit-while-running flow needs its own persistence path.

packages/preset/agent-presets/README.i18n.yaml

@@ -2,5 +2,5 @@
 # side as of the last confirmed-consistent state. Both languages carry equal authority;
 # after editing either side, bring the other along and re-record with:
 #   pnpm run verify-translation-pairing --write packages/preset/agent-presets/README.md
-README.md: 8c95719bead97845519b7a334603005df201a34d
-README.zh.md: c5e2fd3c7896437ddb4a2acdf101cd2e0e0eedaf
+README.md: 1592fba1163448aaedbd482c56962fa07ebc897e
+README.zh.md: ef4512ab93783674890bc9a848e590792a820e8c

packages/preset/agent-presets/src/mount.ts

@@ -61,6 +61,11 @@ class PresetTree extends Include {
    * shipped composition to `[]` the first time a session ends. Persisting a
    * preset is also meaningless: nothing here is user state, and the same file
    * backs every session that names it.
+   *
+   * Dropping the write drops the `loader/config-update` the inherited method
+   * emits with it. Nothing observes one for a preset subtree today, and a
+   * future "edit your preset while it runs" flow needs a deliberate
+   * persistence path rather than this method's return.
    */
   override write(): void {
   }