feat(rag): index the Obsidian memory vault into Qdrant (semantic memory search)

[AlienWalker1995]

Phase 2B of the Obsidian memory system (follows #76): notes the agent stores through the memory-vault MCP become semantically searchable via qdrant_search — one nomic-768 space shared by ingest and query.

What

• v2/plugins/rag/plugin.yaml — mounts the vault read-only at /watch/memory-vault, nested inside the existing watch root, so the recursive watcher/scanner picks it up with zero ingester config. Same ${MEMORY_VAULT_PATH} var the memory-vault MCP mounts (one vault, two interfaces).
• rag-ingestion/ingest.py — hidden-path rule: any path component starting with . is skipped (.obsidian/ workspace JSON, .trash/ soft-deleted notes, .gitkeep stubs), on both the periodic scan and watchdog-event paths.
• v2/plugins/rag/plugin.yaml — llamacpp-embed gains --batch-size 2048 --ubatch-size 2048. Root-cause fix for a live 500 caught during validation: embeddings require each input to fit in one physical batch, and a 400-word markdown chunk routinely exceeds the upstream n_ubatch=512 default (input (556 tokens) is too large to process. increase the physical batch size (current batch size: 512) — CONVENTIONS.md, live).

Validation (live on ordo-v2)

• Throwaway-container gate: ruff clean, 189 passed / 2 skipped (baseline 181/2; +8 new tests: vault ro-mount render, contract-unchanged, CPU shape, embed batch flags, hidden-path unit/scan/refusal).
• Re-rendered in a --gpus all container from --source out/ordo.yaml: compose diff = only the vault mount line + the 4 embed batch-flag lines; llamacpp chat block byte-identical (pin GPU-97fe65ee unchanged). Applied with up -d --no-deps to rag-ingestion and llamacpp-embed only.
• Ingestion proof: documents points 1 → 6 (5 vault notes + smoketest); .obsidian/.trash/.gitkeep.md excluded; the pre-fix 500 on CONVENTIONS.md cleared on the first scan after the batch fix (Ingested memory-vault/CONVENTIONS.md).
• Semantic proof through the qdrant-rag MCP (the agent's channel): query "how should dashboards be validated" → top hit 0.7377 = memory-vault/memories/user/dashboard-validation-by-content.md, the note Hermes itself wrote via the memory-vault MCP in Phase 2A.

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