feat(pipeline): version tag on indexed nodes + diff_versions MCP tool

[isc-tdyar]

Adds version tagging on all indexed nodes and a diff_versions MCP tool for cross-version change detection.

Closes #1062. Depends on #467 (ObjectScript language support) merging first — the Storage node inline-JSON change targets ObjectScript Storage nodes.

New API

cbm_pipeline_set_version(cbm_pipeline_t *p, const char *version_tag)

Sets a version label (e.g. "28.0") on a pipeline instance. When set, the tag is written as a "version" property on every node. Also bypasses the incremental-index path so versioned indexing always does a full pass — the graph accumulates both versions side-by-side.

index_repository tool: new version parameter

{ "repo_path": "/repos/myproject-28.0", "version": "28.0" }

When omitted, a version-like segment (digits and dots) is auto-derived from the repo path. No behavior change for projects that don't use versioning.

diff_versions MCP tool

{
  "project":      "myproject",
  "from_version": "28.0",
  "to_version":   "30.0",
  "label":        "Class"
}

Returns {"added": [...], "removed": [...], "from_version": "28.0", "to_version": "30.0"}. Default label Class, limit 500 per side.

Files changed

• src/pipeline/pipeline.h — cbm_pipeline_set_version() declaration
• src/pipeline/pipeline_internal.h — version_tag field on ctx
• src/pipeline/pipeline.c — setter, free, skip-incremental guard, ctx wiring
• src/pipeline/pass_definitions.c — version property on all nodes; Storage nodes with structured docstring have fields merged inline as raw JSON rather than escaped
• src/pipeline/pass_parallel.c — same changes mirrored; version_tag threaded through parallel worker
• src/mcp/mcp.c — cbm_derive_version_from_path() helper, version param on index_repository, diff_versions tool registered and handler implemented

[DeusData]

The current PR cannot be reviewed against its stated purpose. Its title and body describe version tags and a diff_versions tool, but the branch currently contains the same body-token extractor change as PR #1060 and no versioning or MCP-tool implementation. Please restore the intended branch contents or close this PR if it was superseded; we should not review or merge a title/diff mismatch.

[isc-tdyar]

You were right, the branch did contain the body-token change from #1060 instead of the versioning work. That was a mistake in how I built the branch, not a stale description. It has since been rebuilt from scratch off main with the intended contents, and I've just rebased it again onto current main to clear the merge conflict.

What's in the diff now:

• version_tag plumbed through the pipeline (cbm_pipeline_set_version(), stamped onto nodes at insert time, including the ObjectScript parallel extraction path)
• diff_versions MCP tool: added/removed node detection between two version tags via OPTIONAL MATCH anti-joins
• optional version argument on index_repository, plus derivation from a trailing version-like path segment (/repos/MyApp/28.0 -> 28.0)
• diff_versions registered in TOOL_ANNOTATIONS as read-only, non-destructive, idempotent, and in the annotation-coverage test

Incremental indexing is skipped when a version tag is set, since a version stamp needs a full pass to be coherent.

Sorry for the wasted review cycle on the mismatch. Ready for review when you get to it, and no rush, I know #1063 is also in your queue.