docs: fix OpenAI strict-schema and Bedrock note in office-assistant MVP

Addresses PR review feedback:

- ingest-meeting: OpenAI structured output is sent with strict:true, which
  requires every declared property to appear in `required`. The
  action_items item schema listed description/owner but only required
  title, so the summarize step would 400. Make them required and nullable
  (type: [string, null]) so absent values are expressible.
- docs: the Bedrock swap needs `provider: bedrock` (+ region); provider
  defaults to openai, so changing only credential/model still sends an
  OpenAI-format request. Corrected the guidance.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01WnKgCRfMvFcZAkoVbr8k79

Author: claude

packages/site/src/content/docs/office-assistant-mvp.md

@@ -21,11 +21,17 @@ Create these credentials (`mantle secrets create`) and the KB schema:
 
 | Credential name | Type | Used for |
 | --------------- | ---- | -------- |
-| `openai` | `openai` | `ai/completion` (summarize + answer). Swap the `credential:` and `model:` for `bedrock` to use Claude via Bedrock. |
+| `openai` | `openai` | `ai/completion` (summarize + answer) |
 | `kb-db` | `postgres` | The knowledge-base database |
 | `jira` | `basic` | `jira/create_issue` (email + API token) |
 | `teams` | `generic` | `teams/send_message` (incoming-webhook URL) |
 
+> **Using Claude via Bedrock instead of OpenAI:** in both `ai/completion` steps,
+> add `provider: bedrock` and a `region:` to `params`, point `credential:` at an
+> `aws` credential, and set `model:` to a Bedrock model ID. `provider` defaults
+> to `openai`, so changing only `credential`/`model` still sends an
+> OpenAI-format request.
+
 Apply the KB schema (pure Postgres full-text search, no extensions) from
 [`office-assistant-kb-schema.sql`](https://github.com/dvflw/mantle/blob/main/packages/site/src/content/examples/office-assistant-kb-schema.sql):
 

packages/site/src/content/examples/office-assistant-ingest-meeting.yaml

@@ -54,12 +54,22 @@ steps:
               properties:
                 title:
                   type: string
+                # description/owner are nullable rather than optional: OpenAI
+                # strict structured output requires every declared property to
+                # appear in `required`, so absent values must be expressible as
+                # null instead of being omitted from the schema.
                 description:
-                  type: string
+                  type:
+                    - string
+                    - "null"
                 owner:
-                  type: string
+                  type:
+                    - string
+                    - "null"
               required:
                 - title
+                - description
+                - owner
               additionalProperties: false
           action_items_markdown:
             type: string