BYOK provider embeddings (wave 6 chunk B): kill local transformers

Replace the @huggingface/transformers local embedder (~316MB ONNX cache)
with an EmbeddingPort seam: graph.embeddingModel (nullable "provider:id"
slug) selects an OpenRouter/OpenAI/Gemini adapter, resolved fresh per
call from settings + the auth store so key rotations land immediately.

- src/server/embeddings.ts rewritten: slug grammar, injected-fetch
  adapters (OpenRouter input_type, Gemini taskType batching, OpenAI
  index-ordered rows), honest resolution (null = skip-with-info, set
  model with missing key = honest error), embedNewNodes with model-change
  re-embed wipe + ghost pruning + usage steps, federated catalog
  (OpenRouter /api/v1/embeddings/models — VERIFIED live, the inverse
  path 404s; OpenAI text-embedding- filter; Gemini embedContent filter).
- GET /api/models/embeddings: federated catalog, empty when no keys.
- Extraction tail records stages.embedding usage into the run's money
  channel; EMBEDDING_PRICES overlay in core/prices.ts (outside the
  sync-generated block), callCost falls back to it; cost-summary folds
  the fourth stage; graph-context injection resolves its embedder per
  run, fails honestly when unconfigured, records query tokens.
- Settings: GraphSettings.embeddingModel (null factory), section parser
  validates slug shape (id may contain colons — OpenRouter :free
  suffixes, live catalog fact).
- Removal: @huggingface/transformers uninstalled, PATHS.modelCache and
  onnx tracing entries deleted, @huggingface tracing-excludes guard
  added, stale sharp/libvips comments updated to historical.

Live-verified on port 3004: catalog federates 36 rows (33 OpenRouter +
3 OpenAI), embedNewNodes embedded 10 nodes via the free liquid/lfm-2.5
model (dim 1024, 435 prompt tokens, 1 call, $0), settings PUT rejects
bad slugs with 400.

Gates: typecheck, lint, 895/895 tests, build.

src/agent/subagents/headless.ts

@@ -205,11 +205,13 @@ function svgViewport(svg: string, opts: RenderSvgOptions): { width: number; heig
  *  are an arbitrary SPLIT of one zlib stream, so merging them is the more
  *  standard shape, byte-identical stream, zero re-encoding.
  *
- *  Pure Node on purpose (no sharp): the process already loads transformers'
- *  nested sharp + libvips, and importing the root sharp (Next's optional
- *  dependency) put a SECOND libvips into the process — macOS's ObjC runtime
- *  warns (duplicate GNotificationCenterDelegate, "mysterious crashes").
- *  One native image lib per process; app code carries none. */
+ *  Pure Node on purpose (no sharp): historically the process already carried
+ *  a native image lib via @huggingface/transformers' nested sharp + libvips,
+ *  and importing the root sharp (Next's optional dependency) put a SECOND
+ *  libvips into the process — macOS's ObjC runtime warns (duplicate
+ *  GNotificationCenterDelegate, "mysterious crashes"). The transformers
+ *  embedder died with wave 6 (2026-09-23) but the rule lives on: one native
+ *  image lib per process; app code carries none. */
 export function providerSafePng(png: Buffer): Buffer {
 	const SIG_LEN = 8;
 	if (png.length < SIG_LEN + 12 || png.subarray(0, SIG_LEN).toString("hex") !== "89504e470d0a1a0a") return png;