docs: record embedding, neighbor, and inspect decisions

Co-authored-by: Cursor <cursoragent@cursor.com>

docs/adr/0021-always-scope-collection-names-by-model.md

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+# Always scope Qdrant collection names by Embedding Model id
+
+Every Model Corpus collection is named `{strategy}__{embedding_model_id}_collection`, including the default cloud model (`text-embedding-3-small`). This supersedes ADR-0018’s exception that left OpenAI on legacy unscoped names (`fixed_size_collection`). Uniform naming makes Admin labeling obvious for both Cloud and Local and avoids a special case that confused operators wiping/rebuilding corpora.
+
+## Considered Options
+
+- **Always include model id** — chosen; clear for cloud and local
+- **Keep legacy unscoped names for default cloud only** — ADR-0018; rejected going forward after a from-scratch rebuild
+
+## Consequences
+
+- Process/query create names like `fixed_size__text-embedding-3-small_collection` and `fixed_size__nomic-embed-text-v2-moe_collection`
+- Old unscoped collections are not written anymore; Admin still labels them as legacy default-cloud if they remain until deleted
+- Operators wiping for a clean slate should delete legacy collections before re-processing