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>

.changeset/proud-cranes-click.md

@@ -0,0 +1,5 @@
+---
+type: Changed
+pr: 2173
+---
+**Long-context model names render compactly in the statusline** — the verbose " (1M context)" suffix Claude Code appends to the model display name now collapses to a compact " (1M)" badge (tolerant of future window sizes and the abbreviated "ctx" variant: "(500K context)" → "(500K)", "(1M ctx)" → "(1M)"). Lossless — the long-context signal stays, the 12 characters of width don't. (#2160)