feat: Add APOC export procedures (Neo4j-compatible)

[genezhang]

Summary

Add Neo4j APOC-compatible export procedures that work across all ClickGraph modes: HTTP server, Bolt protocol, and embedded.

Syntax

CALL apoc.export.csv.query("MATCH (u:User) RETURN u.name", "/tmp/users.csv", {})
CALL apoc.export.json.query("MATCH (u:User) RETURN u", "s3://bucket/data.json", {})
CALL apoc.export.parquet.query("MATCH ...", "output.parquet", {compression: "zstd"})

Architecture

• Handler intercept pattern (follows PageRank pattern, not ProcedureRegistry)
• Destination resolver: Maps URI schemes to ClickHouse INSERT INTO FUNCTION table functions
  • Local files → file(), S3 → s3(), GCS → s3(), Azure → azureBlobStorage(), HTTP → url()
• Inner Cypher → SQL pipeline: Parses the Cypher query argument, runs through full planner/optimizer/renderer

Parser Fix

Fixed standalone CALL parsing when inner Cypher contains RETURN/UNION keywords. Replaced naive `input.contains("RETURN")" substring check with try-standalone-first, verify-consumed-everything approach.

Changes

File	Lines	Description
src/procedures/apoc_export.rs	+549	Core module: resolver, format mapping, config, SQL builder, 29 tests
src/server/handlers.rs	+150	HTTP export intercept + translate_cypher_to_sql() helper
src/server/bolt_protocol/handler.rs	+137	Bolt export intercept with inner Cypher pipeline
clickgraph-embedded/src/connection.rs	+127	Embedded handle_export_call() + 3 tests
src/open_cypher_parser/mod.rs	±23	Parser fix for positional args in CALL
Docs	+77	Cypher Language Reference, Embedded Mode wiki, STATUS, CHANGELOG

Tests

• Main crate: 1212 unit + 183 integration + 7 e2e + 30 doc = all passing
• Embedded crate: 39 + 10 + 5 = 54 all passing (including 3 new export tests)
• New tests: 29 unit tests in apoc_export.rs + 3 embedded tests

[Copilot]

Pull request overview

This PR adds Neo4j APOC-compatible export procedures (CALL apoc.export.{csv|json|parquet}.query(cypher, destination, config)) to ClickGraph, enabling users to export query results to local files, S3, GCS, Azure Blob Storage, or HTTP endpoints. It also fixes the standalone CALL parser, which previously failed to parse export calls containing RETURN/UNION in the inner Cypher string.

Changes:

• Core export module (src/procedures/apoc_export.rs): New module implementing destination URI resolution, format mapping, SQL generation, and argument parsing for APOC export procedures, with 29 unit tests.
• Handler intercepts: Export procedure handling injected into the HTTP handler (handlers.rs), Bolt protocol handler (bolt_protocol/handler.rs), and embedded mode connection (clickgraph-embedded/src/connection.rs), each running the inner Cypher through the full planning pipeline.
• Parser fix (src/open_cypher_parser/mod.rs): Replaced naive input.contains("RETURN") check with a try-first-verify-consumed approach, enabling standalone CALL with positional string arguments that happen to contain RETURN or UNION.

Reviewed changes

Copilot reviewed 10 out of 10 changed files in this pull request and generated 7 comments.

Show a summary per file

File	Description
src/procedures/apoc_export.rs	New core module: destination resolver, format mapping, config parsing, SQL builder, 29 tests
src/procedures/mod.rs	Exposes apoc_export as public submodule
src/open_cypher_parser/mod.rs	Parser fix: standalone CALL now correctly handles positional args with inner Cypher strings
src/server/handlers.rs	HTTP export intercept + translate_cypher_to_sql() helper function
src/server/bolt_protocol/handler.rs	Bolt export intercept with inline inner Cypher pipeline
clickgraph-embedded/src/connection.rs	Embedded export handler + 3 new tests
docs/wiki/Cypher-Language-Reference.md	New Export Procedures section with syntax, formats, examples
docs/wiki/Embedded-Mode.md	APOC export usage examples for embedded mode
STATUS.md	Documents APOC export as completed feature
CHANGELOG.md	Records feature addition