Update participant guidance and migration paths #1342

Identity audit, F7. Historical ADR-020 uses starting_conditions; current SDL rejects it in favor of precondition starting_assertions under ADR-079. Other guidance mixes old identity, reward, schema-authority, and execution-profile terminology.

Done when

• Publish a current concept/field crosswalk for identity, affiliation, role, objective owner/assignment, actor/target, resources, implementation selection, and address mappings from Separate participant identity, affiliation, and objective assignment #1338–Specify participant address mappings across authoring, runtime, and evidence #1341.
• Make the starting_assertions migration discoverable. Distinguish assertion truth from condition-probe implementation; keep starting_conditions rejected.
• Explain reward_calculator removal under ADR-073 and the normative authority of published schemas under ADR-009.
• Describe ADR-092's green-role/evaluation restriction as a specific execution-profile rule, not a universal participant definition.
• Show composite participants, shared organizations, resource-only services, service participants, participant targets, and implementation swaps. Execute current-syntax examples and label conceptual alternatives.
• Check guide, reference, migration, editor, and docs-index links. Preserve proposed/accepted/historical ADR statuses and amend pinned decisions only through the governed process.

Authors choose autonomy and identity boundaries; a participant need not expose a deployment/component graph. Declarations alone prove no implementation selection or authority. Do not revive removed aliases or change historical records. Update lineage only if derivation claims change.

Prerequisite: #1341. #219 owns normative specification consistency; #221 owns the author-task walkthrough. Audit publication alone does not deliver ACT-613 or establish measured usability.