feat(FN-2993): merge fusion/fn-2993

Commits merged:
- fix(FN-2993): resolve lint and build verification issues
- fix(FN-2993): address provider registry review feedback
- feat(FN-2993): complete Step 7 — add provider registry
- feat(FN-2993): complete Step 6 — add LLM synthesis provider
- feat(FN-2993): complete Step 5 — add local docs provider
- feat(FN-2993): complete Step 4 — add GitHub provider
- fix(FN-2993): align provider config types with step runner contract
- fix(FN-2993): resolve page fetch test module ordering
- test(FN-2993): expand page fetch coverage for timeout and truncation
- feat(FN-2993): complete Step 3 — add page fetch provider
- fix(FN-2993): align web search provider interface and abort assertions
- feat(FN-2993): complete Step 2 — add web search provider
- feat(FN-2993): complete Step 1 — define provider types and settings fields

Files changed:
packages/core/src/index.ts                         |   2 +-
 packages/core/src/settings-schema.ts               |  11 +
 packages/core/src/types.ts                         |  25 ++
 .../app/components/CustomProvidersSection.tsx      |   1 -
 packages/engine/src/index.ts                       |  19 ++
 .../research/__tests__/provider-registry.test.ts   |  49 +++
 packages/engine/src/research/provider-registry.ts  | 110 +++++++
 .../providers/__tests__/github-provider.test.ts    | 143 +++++++++
 .../__tests__/llm-synthesis-provider.test.ts       | 107 +++++++
 .../__tests__/local-docs-provider.test.ts          |  79 +++++
 .../__tests__/page-fetch-provider.test.ts          |  92 ++++++
 .../__tests__/web-search-provider.test.ts          | 101 +++++++
 .../src/research/providers/github-provider.ts      | 327 +++++++++++++++++++++
 packages/engine/src/research/providers/index.ts    |   5 +
 .../research/providers/llm-synthesis-provider.ts   | 216 ++++++++++++++
 .../src/research/providers/local-docs-provider.ts  | 238 +++++++++++++++
 .../src/research/providers/page-fetch-provider.ts  | 123 ++++++++
 .../src/research/providers/web-search-provider.ts  | 269 +++++++++++++++++
 packages/engine/src/research/types.ts              |  50 ++++
 19 files changed, 1965 insertions(+), 2 deletions(-)

Fusion-Task-Id: FN-2993

packages/dashboard/app/components/CustomProvidersSection.tsx

@@ -5,7 +5,6 @@ import {
   fetchCustomProviders,
   updateCustomProvider,
   type CustomProvider,
-  type CustomProviderConfig,
 } from "../api";
 import { AlertCircle, Loader2, Pencil, Plus, Trash2 } from "lucide-react";
 import { OnboardingDisclosure } from "./OnboardingDisclosure";