docs: serve the concierge and other agents in interactive mode

[ethancjackson]

Summary

• Retitle guide 5 around serving bootcamp agents in interactive mode (adk web), with the concierge as the default target and a table of the other starter / adaptive agents.
• Keep the Coder SSH tunnel as the first half (skip it locally) so the guide no longer tells local users to skip the whole thing.
• Point the atlas chooser, root / implementations / getting-started READMEs, and the concierge notebook at the same walkthrough.

Test plan

• Read guide 5 end to end: Coder users should still get tunnel Steps 1–4; local users should jump to the serving section.
• From the repo root, run uv run adk web implementations/getting_started/concierge_agent and confirm the UI loads at http://localhost:8000 and the concierge answers a path-citing question.
• Optionally confirm uv run adk web implementations/energy_oil_forecasting/ lists starter / analyst / adaptive in the UI dropdown.

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