[ponytail] Drop @anthropic-ai/sdk and three unused graphology packages; collapse openrouter into a route #118

Cut

Drop four npm dependencies and collapse the OpenRouter provider into the generic OpenAI-compatible route.

Findings

• native: @anthropic-ai/sdk has one runtime import (src/_core/llm/providers/anthropic.ts:9, two messages.create calls); the other three tiers already speak the same request shape over fetch. Replace with a fetch POST to https://api.anthropic.com/v1/messages (headers x-api-key, anthropic-version), keep the tool-use response shape the extractors parse, and turn the three import type Anthropic sites into a local type. Removes the dependency and its tree.
• native: graphology-components, graphology-shortest-path, graphology-traversal are in package.json but imported nowhere (rg graphology hits only src/graph/analyzer.ts, which uses graphology, graphology-communities-louvain and graphology-metrics). Remove the three.
• yagni: src/_core/llm/providers/openrouter.ts:36 is one OpenAIRoute literal plus four wrappers that duplicate openai-compatible.ts verbatim, differing only in the tier string. Make the generic wrappers take a route and register OpenRouter as a route constant (~90 lines).

Verification

npm run build and npm run test:run green before and after. npm ls shows no orphaned packages. engram doctor still reports the anthropic and openrouter tiers correctly with and without their keys set. The *-factory tests that stub fetch for the OpenRouter tier keep passing.