feat(sequence-diagram): carry AppMap labels on diagram actions

[kgilpin]

What

Each diagram action (function call, HTTP server/client RPC, SQL query) now records the AppMap labels applied to its callee code object, as a sorted labels?: string[] field — omitted when empty.

// buildDiagram.ts, every callee-based branch
labels: labelsOf(callee),   // [...event.codeObject.labels].sort(), or undefined

Why

Labels live only in the raw AppMap classMap and were dropped on sequence-diagram export. Consumers that wanted them (notably the gold-traces behavioral-diff work, which raises the severity of a detected change when the changed node is security-labeled) had to re-join the diagram against the raw AppMap. This makes the exported diagram self-contained: one source of truth for the analysis.

Design notes

• Not in the digest. labels is not folded into digest/subtreeDigest (those derive from buildStableHash/stableProperties). A pure re-label is therefore not a behavioral change — labels are a classification signal, not a behavioral one.
• No formatter change. formatter/json.ts serializes the whole diagram, so labels flows into --format json automatically. Text/PlantUML are unchanged (could annotate labeled calls later if desired).
• All message types. Applied to ServerRPC / ClientRPC / Query / FunctionCall — anything with a callee code object.

Testing

• yarn test — 40 passed (3 new: label reported on a labeled action, undefined on an unlabeled one, and labels excluded from the digest).
• yarn lint — 0 errors.
• End-to-end against a real Python (Strawberry/SQLAlchemy) AppMap: security-labeled resolvers surface their labels in sequence-diagram --format json:

  _claim_player  => ["security.authorization","security.join_code"]
  _game_by_code  => ["security.authorization","security.join_code"]
  

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