feat: add rag post-reindex acceptance

openspec/changes/rag-breadcrumb-embedding-acceptance/specs/rag-retrieval-evaluation/spec.md

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+## ADDED Requirements
+
+### Requirement: Retrieval evaluation SHALL provide live post-reindex acceptance
+The retrieval evaluation system SHALL provide an opt-in live acceptance flow for validating retrieval behavior after embedding input changes require a knowledge-base reindex.
+
+#### Scenario: Live acceptance requires a running service
+- **WHEN** live retrieval acceptance is run
+- **THEN** it SHALL call the configured Spring Boot retrieval endpoint
+- **AND** it SHALL not be required by the offline fixture baseline
+
+#### Scenario: Live acceptance records retrieval evidence
+- **WHEN** a live retrieval case is executed
+- **THEN** the report SHALL include the query, requested topK, result count, top candidate titles or sources, score labels, and raw response fields needed for review
+
+#### Scenario: Reindex prerequisite is documented
+- **WHEN** a developer prepares to validate breadcrumb-aware embedding behavior
+- **THEN** the repository SHALL explain that existing vectors must be reindexed before live validation can reflect the new embedding text
+
+#### Scenario: Live report is reviewable
+- **WHEN** the live acceptance script completes
+- **THEN** it SHALL write JSON and Markdown outputs that can be inspected or attached to interview evidence