Pinned models don't follow model-family upgrades — new versions get buried in "Other Models"

### Problem

I pin the models I use (e.g. GPT-5.5, Claude Sonnet 5, Claude Opus 4.8). When a newer version of a pinned family ships — say **GPT-5.6** — I would never know:

1. My **pinned entries stay version-locked** to the exact model I pinned (`GPT-5.5`), so the pin never advances to `GPT-5.6`.
2. The new model lands in the collapsed **"Other Models"** overflow, which I rarely expand.

So the pinning feature actively works against discovery: the more I curate, the more likely I am to miss upgrades. Today the only fix is to manually unpin the old version and pin the new one every time a family bumps — micro-management I have to repeat per family (GPT / Opus / Sonnet).

### What I'd expect

**1. Family-aware "latest" pins.** A pin should be able to track *"the latest price-matching model in this family"* rather than a frozen model ID. When GPT-5.6 ships at the same tier as my pinned GPT-5.5, the pin should follow forward automatically (with a subtle affordance that it moved), so I don't have to unpin/re-pin across versions. This is essentially the **"Bump List"** idea from #293875, but user-scoped and tied to pins.

**2. Collapse superseded versions.** If I've pinned/used a family, the always-visible unpinned area (and "Other Models") shouldn't surface *older* versions of that family — only the **latest / recommended** additions. Older versions should still be reachable via search, but not compete for the small amount of visible space.

### Open question: how does "Featured new models" integrate with pinning?

There's already a server-driven **Featured** mechanism (from the `chat.modelsControl` manifest) that surfaces new models in the Promoted section, and #317128 notes that section is "doing two jobs" (Recent behavior + server marketing). It's unclear how that competes with or complements pinning:

- If I've pinned GPT-5.5 and GPT-5.6 is featured, do I get a duplicate/promoted row *and* a stale pin?
- Should featuring a new family version instead **offer to advance my existing pin** (the bump behavior above) rather than adding a separate entry?

### Related

- #317128 (Model Management UX Exploration — umbrella)
- #293875 (Enhance Models Picker — mentions the "Bump List")
- #283751 (opinionated picker — latest-per-family defaults)
- #299776 (Add model pinning)
- #298063 (remove visibility as a concept)

/cc @sandy081 @eli-w-king