feat: bash-backed glob/grep discovery tools (dsh-tool-fs-search)

Implements docs/rfc/implemented/feature/2026-07-09-bash-backed-grep-glob-
discovery.md: model-facing glob/grep in a new @deepseek-ai/dsh-tool-fs-search
package, executing fixed ripgrep templates through ctx.bash.resolve/run —
not ctx.fs provider methods — so filesystem backends stay free of a search
contract and sandboxed/remote executors substitute cleanly. The tools never
call ctx.bash.start(); the tool layer owns quoting (one singleQuote safety
boundary), rg --json parsing, ItemRetainer/TextRetainer retention, and the
first tool-owned ctx.spillFiles.saveText() handoff (item-level retention the
generic post-execute spill policy cannot recover).

RFC amendments on the way to implemented/: a shared src/search-core.ts (the
SEARCH_* vocabulary + bash-run/raw-spill/spill plumbing was byte-identical
across both tools — the missed-extraction smell), and a snapshot-gap note:
wiring the acp-agent tree changes the assembled prompt, so goldens need a
keyed re-record; the spill notice text is pinned by unit tests instead and
only the coding-agent example ships the tools for now.

knip.json

@@ -83,6 +83,11 @@
     "packages/fs/tool-fs": {
       "entry": ["tests/**/*.spec.ts", "tests/**/*.e2e.ts"],
       "project": ["src/**/*.ts", "tests/**/*.ts"]
+    },
+    "packages/fs/tool-fs-search": {
+      "entry": ["tests/**/*.spec.ts"],
+      "project": ["src/**/*.ts", "tests/**/*.ts"],
+      "ignoreBinaries": ["rg"]
     }
   }
 }