fix(terminal): merge-time fixes for the copy gutter strip (#469)

- stock.ts: claude is no longer the only entry declaring transcriptGutter;
  codex declares it too.
- architecture-invariants: the strip applies when the session's CLI declares
  a margin (not detection), and a note that it keys on the session's launch
  mode, not on what is running in the pane (a claude pane dropped to a shell
  still loses up to two columns; copyStripMargin is the escape hatch).
- render-index-html test: the gutter map is injected for a solo
  /session/:id render as well.

Co-Authored-By: Claude Opus 5.5 (1M context) <noreply@anthropic.com>

src/config/cli-registry/stock.ts

@@ -214,8 +214,8 @@ const CLAUDE: CliEntry = {
   capabilities: {
     external: false,
     // Claude indents its transcript body two columns and puts its own ●/✻/❯ markers
-    // in them, so a copy can drop two and paste flush. The only entry that declares
-    // this, because it is the only one whose gutter has been measured.
+    // in them, so a copy can drop two and paste flush. Claude and codex are the only
+    // entries that declare this, because theirs are the only gutters that have been measured.
     transcriptGutter: 2,
     // The historical hard-coded pair, now stated as data. `workingLine` matches both the
     // `✻ Actualizing… (39s · ↓ 2.0k tokens)` status line and the bare `esc to interrupt`