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.

tsconfig.base.json

@@ -34,8 +34,6 @@
       "@cordisjs/plugin-timer": ["./vendor/timer/src"],
       "@cordisjs/plugin-hmr": ["./vendor/hmr/src"],
       "@cordisjs/plugin-logger-console": ["./vendor/logger-console/src"],
-      "@deepseek-ai/dsh-tool-web/search": ["./packages/web/tool-web/src/search.ts"],
-      "@deepseek-ai/dsh-tool-web/fetch": ["./packages/web/tool-web/src/fetch.ts"],
       // One wildcard maps every @deepseek-ai/dsh-<name> to its source. Package
       // dir names are unique across groups, so first-on-disk-wins resolution is
       // unambiguous; adding a package under an existing group needs no edit