fix: address codex review findings on web seam

- search providers (exa/perplexity/deepseek): map the parsed response
  INSIDE the parse try, so a well-formed body of the wrong shape surfaces
  as WEB_PROVIDER_ERROR instead of escaping as a raw TypeError; a WebError
  the mapper throws on purpose is re-thrown untouched
- web-fetch-local: validate numeric limits at plugin construction (positive
  finite caps; non-negative integer maxRedirects) rather than constructing a
  provider with nonsensical values
- web-fetch-local: enforce the redirect budget BEFORE resolving each hop, so
  maxRedirects:N follows exactly N redirects and an over-limit hop reports
  "exceeded the maximum" rather than misdiagnosing a cross-origin block
- drop the stale dsh-tool-web/search and /fetch path aliases (the package no
  longer declares those subpath exports)
- strip trailing EOF blank lines flagged by git diff --check

Each fix carries a regression test.

packages/web/web-search-perplexity/tests/perplexity.spec.ts

@@ -116,6 +116,12 @@ describe('PerplexitySearchProvider error handling', () => {
       .rejects.toThrow(expect.objectContaining({ message: 'bad request' }))
   })
 
+  it('maps a well-formed body of the wrong shape to WEB_PROVIDER_ERROR, not a raw TypeError', async () => {
+    vi.stubGlobal('fetch', vi.fn(async () => jsonResponse({ search_results: null }, { status: 200 })))
+    await expect(new PerplexitySearchProvider(options).search({ query: 'q' }))
+      .rejects.toThrow(expect.objectContaining({ code: 'WEB_PROVIDER_ERROR' }))
+  })
+
   it('keeps a status-line message when the error body is not JSON', async () => {
     vi.stubGlobal('fetch', vi.fn(async () => new Response('upstream error', { status: 503 })))
     await expect(new PerplexitySearchProvider(options).search({ query: 'q' }))