fix(codex): retire deprecated web-search flag behind one CODEX_WEB_SEARCH_FLAG constant (#2525)

codex >=0.144 deprecates the legacy --enable-based web_search_cached
spelling (web search is on by default; --enable <FEATURE> now means
-c features.<name>=true, verified against codex 0.147.0's exec --help).
Every gstack codex invocation now passes -c 'web_search="cached"' instead.

The flag previously lived inline at 19 raw sites. Per ENG-OV11a the 10
template-inline sites (autoplan/SKILL.md.tmpl x4, codex/SKILL.md.tmpl x6)
convert to a shared {{CODEX_WEB_SEARCH_FLAG}} token first, so ONE resolver
constant (CODEX_WEB_SEARCH_FLAG in scripts/resolvers/constants.ts) now
covers all sites: review.ts x5, design.ts x3, the token resolver in
utility.ts, and the tool-map helper comment.

codex/SKILL.md.tmpl's web-search prose guarantee is corrected: the -c form
explicitly overrides a top-level web_search config (the legacy flag yielded
to it), and native codex review disables web search regardless of
configuration, so the flag is a no-op on the default Review path.

test/codex-web-search-flag.test.ts is the safety net: repo-wide grep
tripwires assert NO rendered SKILL.md/section/golden and NO source file
carries the deprecated spelling, and that the token resolves in rendered
output.

Fixes #2525

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

test/helpers/tool-map.ts

@@ -50,7 +50,7 @@ export const TOOL_COMPATIBILITY: Record<'claude' | 'gpt' | 'gemini', Record<Tool
     Glob: false,
     Grep: false,
     AskUserQuestion: false,
-    WebSearch: true,    // --enable web_search_cached
+    WebSearch: true,    // -c 'web_search="cached"' (CODEX_WEB_SEARCH_FLAG, #2525)
     WebFetch: false,
   },
   gemini: {