refactor(tools): break glob->grep sibling-tool coupling

Hoist shared ripgrep CLI resolution helpers (resolveGrepCli, resolveGrepCliWithAutoInstall, GrepBackend, DEFAULT_RG_THREADS, ResolvedCli) out of src/tools/grep/constants.ts into src/shared/ripgrep-cli.ts so they no longer straddle two sibling tool directories.

Before: src/tools/glob/constants.ts re-exported from src/tools/grep/constants.ts, violating the project's "tools should not import from sibling tools" rule enforced by .sisyphus/rules/modular-code-enforcement.md.

After: both src/tools/glob/ and src/tools/grep/ consume the shared helpers from src/shared/ripgrep-cli.ts. src/tools/grep/constants.ts keeps only the grep-specific UI-exposed constants.

src/tools/grep/cli.ts

@@ -3,13 +3,15 @@ import {
   resolveGrepCli,
   type ResolvedCli,
   type GrepBackend,
+  DEFAULT_RG_THREADS,
+} from "../../shared/ripgrep-cli"
+import {
   DEFAULT_MAX_DEPTH,
   DEFAULT_MAX_FILESIZE,
   DEFAULT_MAX_COUNT,
   DEFAULT_MAX_COLUMNS,
   DEFAULT_TIMEOUT_MS,
   DEFAULT_MAX_OUTPUT_BYTES,
-  DEFAULT_RG_THREADS,
   RG_SAFETY_FLAGS,
   GREP_SAFETY_FLAGS,
 } from "./constants"