Newly launched models default to full effort instead of a launch-time pin

What

• Claude Code used to force newly launched models (like a brand-new Opus or Fable release) to run at a reduced "launch effort" level for a period after release, controlled by settings such as unpinOpus47LaunchEffort, unpinOpus48LaunchEffort, and unpinFable5LaunchEffort.
• A new mechanism now walks the list of newly-launched models (claude-opus-4-7, claude-opus-4-8, claude-fable-5, and whatever ANTHROPIC_DEFAULT_FABLE_MODEL resolves to) and keeps each pinned to the launch effort level unless the matching unpin setting is turned on.
• For a genuinely first-ever install of this build (no firstStartVersion recorded yet), the whole pin list is skipped, so brand-new installs start unpinned.
• The three unpin settings were removed from the default client config store, and the model-recency list used for feature gating now includes claude-opus-4-6, claude-opus-4-7, claude-opus-4-8, and claude-sonnet-4-6.

Why

This keeps existing installs behaving the same (still pinned to a conservative effort level for brand-new models) while letting fresh installs and future models participate in feature gating and default effort without extra config.