feat(web): a prose mention of a produced file opens it

The chatFileMentions service (provided by ui-deliverables beside its
turn-tail entry, reached via ctx.get) resolves inline-code tokens in the
closing message against the turn's produced locations: exact path or
unique basename links, ambiguity and unknowns stay inert. MarkdownText
gains the optional fileMentions seam — settled renders only, never
inside anchors.

apps/web/tsconfig.json

@@ -61,6 +61,7 @@
     "tests/shipped-composition.e2e.ts",
     "tests/startup-auto-selection.e2e.ts",
     "tests/produced-files.e2e.ts",
+    "tests/produced-file-mentions.e2e.ts",
     "tests/goal-bar.e2e.ts",
     "tests/subagent-conversation.e2e.ts",
     "tests/bash-abort-row.e2e.ts",