feat(#2160): collapse verbose '(1M context)' model suffix to compact (1M) badge (#2173)

* feat(#2160): collapse verbose '(1M context)' model suffix to compact (1M) badge

Claude Code appends " (1M context)" to the model display name in
long-context sessions, eating 12 characters of statusline width. Collapse
it to " (1M)" — the signal stays, the width doesn't. Any other display
name passes through unchanged.

Claude-Session: https://claude.ai/code/session_01Hme55Pvq6BhpgwBcyC5HAg

* docs(#2160): changeset fragment for PR #2173

* fix(#2160): review fixes — ctx variant, boundary test, changeset format

- broaden the suffix match with a context|ctx alternation (approval-condition
  variant the regex missed)
- pin non-context parentheticals ((beta), (deprecated)) as untouched
- changeset body ends with the (#2160) citation per house convention

Claude-Session: https://claude.ai/code/session_01Hme55Pvq6BhpgwBcyC5HAg

* test: regenerate golden-install-parity fixtures for the statusline hook change

Claude-Session: https://claude.ai/code/session_01Hme55Pvq6BhpgwBcyC5HAg

---------

Co-authored-by: Tom Boucher <trekkie@nomorestars.com>

tests/fixtures/golden-install-parity/opencode.json

@@ -399,7 +399,7 @@
   "hooks/gsd-read-guard.js": "9e423cd03e2d1b16",
   "hooks/gsd-read-injection-scanner.js": "f72060dfe035f706",
   "hooks/gsd-session-state.sh": "e54379ba86bf1b6d",
-  "hooks/gsd-statusline.js": "6fcb59ad86d2d0ea",
+  "hooks/gsd-statusline.js": "f93d64704cba14fd",
   "hooks/gsd-update-banner.js": "55143a25f978f301",
   "hooks/gsd-validate-commit.sh": "bf5dd61d33cb3a38",
   "hooks/gsd-windsurf-pre-command.js": "948be1c6d14c79cd",