Add conversation starters authoring guidance to architect

[alicja-gilderdale]

Summary

Adds authoring guidance for conversationStarters to the Copilot Studio Architect agent (agents/copilot-studio-architect.md).

Motivation

The modern cliagent-1.0.0 schema accepts a conversationStarters block under configuration.agentSettings alongside instructions, but the architect agent's guidance does not currently instruct authors to populate it. As a result, agents generated by the architect land in Copilot Studio with an empty starter-prompt picker and the maker has to set them manually via the UI after every push.

Empirically verified against a freshly authored CLI-authoring agent using cliagent-1.0.0 and the Sonnet46 model series.

What changed

• New section ## Conversation Starters in agents/copilot-studio-architect.md (placed between ## Settings YAML and ## Knowledge YAML)
• Documents the exact YAML shape under configuration.agentSettings.conversationStarters, using the same title / text fields as the classic default-2.1.0 schema
• Includes rules on count (3-6), title style (1-4 words), text style (literal prompt with placeholders), and the anti-pattern of embedding starter prose inside instructions

Verification (round-trip test)

Confirmed against a live modern agent:

1. Authored settings.mcs.yml with a conversationStarters block containing 4 entries (title + text)
2. pac copilot push succeeded (1 change(s) pushed)
3. pac copilot pull re-emitted identical YAML (Pull complete. 0 change(s) applied.)
4. Compiled .mcs/botdefinition.json under entity.configuration.agentSettings.conversationStarters contained all 4 entries with matching title and text
5. Pushing again after the pull was a no-op (No local changes detected)

Exact YAML that round-trips cleanly:

configuration:
  agentSettings:
    model:
      series: Sonnet46
    instructions:
      segments:
        - kind: StaticSegment
          value: |
            <instruction body>
    conversationStarters:
      - title: Draft a PID
        text: "Draft a PID from this meeting: <link>"
      - title: Draft Minutes
        text: Turn this transcript into Minutes in the standard template

Scope

Documentation-only. No changes to plugin agents, commands, hooks, or scripts. The architect follows the guidance the next time it generates or edits a settings.mcs.yml.

Testing

• Existing agent files: no schema regression (only additive guidance in the architect markdown)
• Manual verification described above
• No new dependencies

Related work

• Plugin version at time of contribution: mcs-assistant@copilot-studio-plugin v1.0.2
• PAC CLI at time of contribution: 2.9.3+ga17df1d

[Giorgio Ughini (GiorgioUghini)]

I'd want to check if we had starter prompts in classic agents, before creating new ones with the architect agent. We should do this in migrate.md