feat(agent-interface): centralize harness↔model snapping; fix nanoclaw capabilities

[vutuanlinh2k2]

What

Makes @tangle-network/agent-interface the single source of truth for harness↔model
snapping, and corrects nanoclaw's capabilities.

Changes (packages/agent-interface/src/harness-capabilities.ts)

• nanoclaw is router-backed, not Anthropic-locked. Removed nanoclaw: ["anthropic"] from
  harnessProviderLock. Its runner routes every provider through the Tangle router
  (TANGLE_ROUTER_MODEL + OpenAI/OpenRouter/Anthropic base URLs all → gateway), so it runs any
  model like opencode. harnessSupportsModel("nanoclaw", <anything>) is now true.
• nanoclaw reasoning ceiling ultracode → none. Its runner sends no thinking flag, so
  reasoningEffortsFor("nanoclaw") now returns ["none"] instead of over-advertising the full ladder.
• Added the catalog-snap layer (previously hand-rolled, identically, in both sandbox-ui and
  agent-app): snapModelToHarness(harness, modelId, candidateIds) and
  snapHarnessToModel(harness, modelId), plus a private harnessPreferredModelPatterns ranking
  table. Both reuse the existing harnessSupportsModel / preferredHarnessForModel and are
  catalog-agnostic (take readonly string[] of canonical ids), so consumers can delete their forks.

Supporting

• New src/harness-capabilities.test.ts (16 cases): compatibility + aliases, nanoclaw = any model,
  snap ranking (opus-before-sonnet, gpt-frontier-before-mini), the router-backed "don't snap" path,
  reasoning ceilings (incl. nanoclaw = none), and model-capability narrowing.
• package.json: test / test:watch scripts + vitest devDep (catalog).
• tsconfig.json: exclude *.test.ts from the build so tests don't ship in dist.
• Changeset → minor (0.14.0 → 0.15.0): new exports + the nanoclaw behavior change.

Why

The harness↔model compatibility rule (and the snap helpers) were hand-copied into three places
that disagree — agent-interface, sandbox-ui/src/chat/harness-model-compat.ts, and
agent-app/src/harness/index.ts. Today the two consumers don't even call agent-interface's
copy, so its wrong nanoclaw lock is dead code; it would become a live regression the moment they
migrate. This PR fixes nanoclaw and lands the snap helpers here first, so the consumer PRs can
delete their forks and import from one source.

Verification

• pnpm --filter @tangle-network/agent-interface build — clean; no test files in dist.
• check-types — passes.
• pnpm --filter @tangle-network/agent-interface test — 16/16 pass, single run.
• Swept the monorepo: nothing else depends on nanoclaw's old lock.

Scope / follow-ups

First of a multi-repo unification tracked in tangle-network/gtm-agent#395:

1. (this PR) agent-interface: fix nanoclaw + add snap helpers.
2. sandbox-ui: rewrite harness-model-compat.ts to delegate to these exports (keep its 5 public
   re-exports stable).
3. agent-app: add agent-interface as a peerDep; delegate the policy via a documented as HarnessType
   boundary cast (its Harness taxonomy — forge/cursor — diverges; full taxonomy unification is a
   separate follow-up).
4. gtm-agent: dep bumps only.

Draft until 0.15.0 is published and the consumer PRs are validated against it.