feat(terminal): auto-abbreviate to short codes + legend on overflow - #20

Stacked on #19 (base is render-json-example, since skills/cmg/SKILL.md is introduced there). Merge #19 first, then rebase this onto main.

What

In the default auto direction, when a compact chain or diamond would exceed the column budget, node labels are replaced with short, deterministic codes and a Legend block mapping each code back to its full name is appended. A near-linear flow now stays one readable row instead of collapsing into the stacked vertical node-list + Edges fallback.

┌────┐    ┌─────┐    ┌─────┐    ┌─────┐    ┌─────┐
│ CT │───▶│ CMG │───▶│ MGR │───▶│ GRT │───▶│ RRV │
└────┘    └─────┘    └─────┘    └─────┘    └─────┘

Legend
  CT = createTransform
  CMG = createModelGraph
  MGR = ModelGraph run
  GRT = GraphRun trace
  RRV = renderRun view

How

• Codes derive from the names — word initials, or first-letter + leading consonants for a single word — de-duped in node order with the shortest numeric suffix on collision. Nothing is invented; the legend is just the node's own label.
• Scoped to auto. Explicit direction:"horizontal" keeps its strict requires N columns error contract; explicit vertical is untouched. The behavior slots into a previously-uncovered middle column band, so no existing test moves.
• Fallback preserved — if codes still don't fit, it falls to the vertical list exactly as before.

Parity & tests

• Mirrored byte-identically in the Python twin (terminal/__init__.py) per the language-parity law; verified TS↔Python identical on chain-overflow, diamond-overflow, and narrow-vertical-fallback.
• One new parity test in each suite (terminal.test.ts 18 ✓, test_terminal.py 10 ✓). Typecheck clean; example-19 snapshot unchanged.

Skill doc

skills/cmg/SKILL.md gains a note that full names are now fine in auto mode (the renderer abbreviates + legends automatically). This diff also folds in the earlier, still-uncommitted "paste inside a code fence" rendering guidance (fixes the proportional-font wrapping seen in GUI chats like Codex).