[Chore] Build agent inventory and responsibility boundary map

[jerry609]

Goal

Build a complete inventory of all current agent entrypoints and define responsibility boundaries.

Scope

• Inventory route/workflow entrypoints that invoke agents
• Mark each flow as must_use_agent or service_preferred
• Document owner, input/output, SLA, fallback path
• Output to docs/agent_inventory.md

Acceptance

• Every current agent entrypoint is listed
• Each entry has boundary + fallback
• Decision rules for Agent vs Service are explicit

[jerry609]

Completed in commit 3efceb7 on branch feat/harvest-aligned-base-v2.