docs: reflect Foundry's :2 first-publish version in prompt-agent quickstart

[placerda]

Fixes a couple of accuracy bugs in the prompt-agent quickstart tutorial that surfaced during a real run-through.

What was wrong

1. First-publish version is :2, not :1. When you save+publish a prompt agent for the first time in the Foundry portal, Foundry numbers the unpublished draft as :1 and assigns :2 on first publish. The tutorial assumed :1 throughout the sandbox-author narrative, so the seed pointer in agentops.yaml, the wizard prompt, and the playground walkthrough were all off by one.
2. Example foundry-agent.json had the wrong field names. The tutorial showed agent_source / agent_candidate and a nested agentops.* block. pipeline/prompt_deploy.py actually writes flat source_agent / candidate_agent / prompt_sha256 / git_sha / workflow_url. Anyone copying the example to script against would break.

What changed

• All sandbox-author references updated from travel-agent:1 to travel-agent:2: prereqs row, mental-model diagram, journey table, microsoft-foundry skill prompt (Path B), section 4 header + Save callout, section 5 playground, section 7 init wizard, section 9 agentops.yaml example, and the section 11 PR-workflow narrative.
• Section 13 example foundry-agent.json rewritten to match what the deploy artifact actually contains today (flat field names, full set of identifiers).
• Added a callout explaining the SDK vs. portal version-numbering asymmetry: because CI uses the Foundry SDK and starts at :1 in an empty project, the bootstrap may fire on the first one or two deploys per environment before the env catches up to the sandbox seed (:2). After that, normal reuse/create flow takes over. The durable identity is prompt_sha256 + git_sha, not the per-project version numbers — the existing mental-model section already says this; the new callout just makes the practical consequence explicit so readers don't think CI is misbehaving when they see action: bootstrapped twice in a row.
• Success criteria and Where to go next blocks updated to drop stale travel-agent:1 claims about the dev seed.

Validation

• python -m pytest tests/unit/test_prompt_deploy.py -x -q → 7 passed.
• Cross-checked docs/tutorial-end-to-end.md — already says travel-agent:2 after first publish (line 181). No change needed there.
• docs/tutorial-hosted-agent-quickstart.md does not mention prompt-agent version numbers — no change needed.

Out of scope

• No code change. prompt_deploy already handles the bootstrap-fires-twice case correctly; the only ask was that the tutorial stop misrepresenting what the user will observe.