fix: drop tool-web subpath exports, align with tool-bash single-entry shape

The web tool package exposed ./search and ./fetch as standalone subpath
plugins, but nothing consumed them, the RFC never called for them, and the
sibling dsh-tool-bash (also a multi-tool consumer) ships a single entry and
selects tools via config. The extra entries also tripped the workspace
constraints gate, whose expected `files` list covers single-entry and bin
packages but not a non-bin multi-entry one.

Collapse to a single `.` entry: drop the ./search|./fetch exports and their
lib/*.js from package.json files, delete the per-package tsdown override (the
root config's lib/types/index.js entry now suffices), and remove the
plugin-shaped name/inject exports from search.ts/fetch.ts (renaming each
apply to its applyWeb{Search,Fetch}Tool helper, still composed by the root
plugin and re-exported from the index). Selective enablement stays via the
existing { search?, fetch? } config. Docs updated to match.

packages/web/tool-web/package.json

@@ -11,21 +11,11 @@
       "types": "./lib/types/index.d.ts",
       "default": "./lib/index.js"
     },
-    "./search": {
-      "types": "./lib/types/search.d.ts",
-      "default": "./lib/search.js"
-    },
-    "./fetch": {
-      "types": "./lib/types/fetch.d.ts",
-      "default": "./lib/fetch.js"
-    },
     "./src/*": "./src/*",
     "./package.json": "./package.json"
   },
   "files": [
     "lib/index.js",
-    "lib/search.js",
-    "lib/fetch.js",
     "lib/types/**/*.d.ts",
     "lib/types/**/*.d.ts.map",
     "src"