feat: add node update endpoint and table LLM context fields

[ajainvivek]

Summary

• New endpoint PATCH /v1/documents/:id/nodes/:node_id — update individual document nodes (title, summary, content, image_path, and all metadata fields including attributes and cross-references)
• Table LLM context fields — added domain_vocab, context, instructions, and tags as first-class fields on the Table model; exposed via the existing PATCH /v1/tables/:id endpoint
• Docs updated — OpenAPI spec, utoipa Swagger UI registration, and the Tables guide all reflect the new endpoints and fields

Changes

crates/reasondb-core/src/model/table.rs

• Added domain_vocab: Option<Vec<String>> — domain terms for LLM reasoning
• Added context: Option<String> — contextual description for LLM
• Added instructions: Option<String> — custom LLM query/reasoning directives
• Added tags: Option<Vec<String>> — classification tags

crates/reasondb-server/src/routes/tables.rs

• Extended UpdateTableRequest and TableResponse with the 4 new fields
• Handler applies each field when Some(...)

crates/reasondb-server/src/routes/documents.rs

• Added UpdateNodeMetadataRequest, UpdateNodeRequest, NodeDetail structs
• Added update_node handler with ownership validation (node must belong to the given document)

crates/reasondb-server/src/routes/mod.rs

• Registered PATCH /v1/documents/:id/nodes/:node_id

docs/api-reference/openapi.json

• Updated UpdateTableRequest and TableResponse schemas
• Added UpdateDocumentRequest, UpdateNodeMetadataRequest, UpdateNodeRequest, NodeDetail schemas
• Added PATCH operation to /v1/documents/{id}
• Added /v1/documents/{id}/nodes/{node_id} path with PATCH operation

docs/guides/tables.mdx

• Updated Table Schema table with new fields
• Added "Configuring LLM Context" sub-section with curl examples

crates/reasondb-server/src/openapi.rs

• Registered update_document and update_node in utoipa ApiDoc

Test plan

• PATCH /v1/tables/:id with domain_vocab, context, instructions, tags — verify fields are persisted and returned in GET /v1/tables/:id
• PATCH /v1/documents/:id/nodes/:node_id with title, summary, content — verify updated node returned
• PATCH /v1/documents/:id/nodes/:node_id with metadata.attributes — verify attributes are merged not replaced
• PATCH /v1/documents/:id/nodes/:wrong_doc_id — verify 404 when node doesn't belong to document
• Confirm Swagger UI at /swagger-ui shows new endpoints and schemas