refactor(tool-fs): drop per-tool subpath plugins; adopt single-tsconfig build

Adapt the four fs packages to master's single-tsconfig build convention
(lib/types outDir + types path + files allowlist), brought in by the merge.

While doing so, drop dsh-tool-fs's /read//write//edit subpath plugins. They
were the only subpath-export package in the tree and forced bespoke tsdown,
tsconfig path, package.json files, and workspace-constraint handling that no
sibling tool package (e.g. dsh-tool-bash) carries, for a focused-deployment
use case no consumer needed. dsh-tool-fs is now a single root plugin that
registers read/write/edit, mirroring dsh-tool-bash; the per-tool registration
helpers stay internal modules the root composes. The file-context event-gate
RFC is amended to record the narrowed scope.

packages/fs/tool-fs/package.json

@@ -11,23 +11,13 @@
       "types": "./lib/types/index.d.ts",
       "default": "./lib/index.js"
     },
-    "./read": {
-      "types": "./lib/types/read.d.ts",
-      "default": "./lib/read.js"
-    },
-    "./write": {
-      "types": "./lib/types/write.d.ts",
-      "default": "./lib/write.js"
-    },
-    "./edit": {
-      "types": "./lib/types/edit.d.ts",
-      "default": "./lib/edit.js"
-    },
     "./src/*": "./src/*",
     "./package.json": "./package.json"
   },
   "files": [
-    "lib",
+    "lib/index.js",
+    "lib/types/**/*.d.ts",
+    "lib/types/**/*.d.ts.map",
     "src"
   ],
   "license": "BSD-3-Clause",