feat: replace_matching_properties — bulk property edit (closes #127)

[vicmaster]

Closes #127.

What

New MCP tool replace_matching_properties: find every node whose properties equal all the match entries and apply the set properties to each in one call — the "set width: "100%" on all nodes currently width: 110" case from the issue becomes one line instead of 68 hand-authored U() ops.

replace_matching_properties({
  canvasId,
  match:  { width: 110 },     // AND across keys; $token refs match literally; structured values (shadows, gradient) by shape
  set:    { width: "100%" },  // id/type stripped, same safety rule as U()
  scope?: "nodeId",           // limit to a subtree (inclusive)
  type?:  "text",             // node-type filter
  dryRun?: true               // preview matched nodes + count without writing
})

Returns { ok, count, matches: [{ id, type, name? }] } (+ dryRun: true on previews). Refuses an empty match (would match every node) and an empty set (unless dryRun). ensureFresh runs before the mutation like every other mutating tool.

Implementation

• src/scene-graph.ts — pure core: collectMatchingNodes (document-order walk, scope-inclusive) + replaceMatchingProperties; propEquals is strict for primitives, JSON-shape for structured values.
• src/index.ts — thin handler after batch_design; viewer URL on real writes only.
• Agent surfaces (same PR, per the discoverability rule) — tool docstring, server INSTRUCTIONS paragraph, GOTCHAS entry, README section, GUIDELINES "Sharp edges" bullet, VISION checklist entry.

Testing

• test-replace-matching.ts — 14/14: AND matching, token-ref + structured-value matching, scope/type filters + decoys, scope-inclusivity, missing-scope throw, replace mutation, id/type stripping.
• test-discoverability.ts — 14/14 (48 tools).
• Regression: test-ops-parser, test-batch-design-idmap, test-feedback, test-init all pass; tsc clean.
• docs-steward audit run pre-PR (one fix: README return shape now notes the dryRun marker).

Not included

The search_all_unique_properties-style companion (enumerate distinct values in use) noted in the issue as prior art — dryRun covers the preview need; the enumerator can be a follow-up if wanted.