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.

tests/data-dir-seam.test.ts

@@ -19,7 +19,7 @@ const REPO_ROOT = path.resolve(import.meta.dirname, "..");
 const TSX_LOADER = path.join(REPO_ROOT, "node_modules", "tsx", "dist", "loader.mjs");
 
 describe("LH_DATA_DIR seam", () => {
-	it("relocates data/chats/graph + modelCache under LH_DATA_DIR, keeps prompts ROOT-anchored", async () => {
+	it("relocates data/chats/graph under LH_DATA_DIR, keeps prompts ROOT-anchored", async () => {
 		const dir = fs.mkdtempSync(path.join(os.tmpdir(), "lh-seam-"));
 		process.env.LH_DATA_DIR = dir;
 		try {
@@ -27,7 +27,6 @@ describe("LH_DATA_DIR seam", () => {
 			assert.equal(PATHS.data, dir, "PATHS.data resolves the env value (resolved absolute)");
 			assert.equal(PATHS.chats, path.join(dir, "chats"));
 			assert.equal(PATHS.graph, path.join(dir, "graph"));
-			assert.equal(PATHS.modelCache, path.join(dir, "models"), "the HF model cache follows the seam");
 			assert.equal(
 				PATHS.teacherPrompt,
 				path.join(ROOT, "src", "agent", "system-prompt.md"),
@@ -41,12 +40,11 @@ describe("LH_DATA_DIR seam", () => {
 	it("unset = the repo data/ exactly as before (fresh child process, no env)", () => {
 		const out = execFileSync(
 			process.execPath,
-			["--import", TSX_LOADER, "--eval", `const m = await import(${JSON.stringify(path.join(REPO_ROOT, "config.ts"))}); console.log(JSON.stringify({ data: m.PATHS.data, chats: m.PATHS.chats, modelCache: m.PATHS.modelCache }));`],
+			["--import", TSX_LOADER, "--eval", `const m = await import(${JSON.stringify(path.join(REPO_ROOT, "config.ts"))}); console.log(JSON.stringify({ data: m.PATHS.data, chats: m.PATHS.chats }));`],
 			{ cwd: REPO_ROOT, encoding: "utf-8" },
 		);
-		const parsed = JSON.parse(out) as { data: string; chats: string | null; modelCache: string | null };
+		const parsed = JSON.parse(out) as { data: string; chats: string | null };
 		assert.equal(parsed.data, path.join(REPO_ROOT, "data"));
 		assert.equal(parsed.chats, path.join(REPO_ROOT, "data", "chats"));
-		assert.equal(parsed.modelCache, null, "dev keeps the transformers package default cache");
 	});
 });