fix(custom-model): warn when parallel llama.cpp slots leave too little context per request (#658)

Squash of PR #658. Discovery records each llama.cpp model's parallel slot
count (from --parallel/-np, or /props total_slots when the launch command
states none), and a Claude launch warns when the context split across
those slots leaves less than 40K tokens per request. An explicit
--parallel beside a /props context records a slot count of 1, so a later
round overwrites an earlier count, and a non-2xx /props is remembered per
launch command while a network error is retried.

Merge-time fix by the maintainer: the architecture-invariants sentence on
the explicit --parallel case now says it records a slot count of 1.

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

.changeset/slot-aware-context.md

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+---
+'aicodeman': patch
+---
+
+A custom llama.cpp model whose parallel slots share a context pool too small for concurrent Claude Code requests now gets an in-app warning. Four simultaneous 40K-token requests against a 4-slot ~131K pool all failed with "Context size has been exceeded" while the old total-context check stayed silent. Discovery records each model's slot count (from `--parallel`/`-np`, or `/props` `total_slots` when the launch command states none) and the warning names the fix: `--parallel 1`, or a context large enough for every slot.