feat(server): surface provider model deprecations to admins and operators

[FelixTJDietrich]

Problem

Provider model retirements break unattended deployments on a schedule nobody in the deployment chose: Anthropic retires models with ≥60 days' notice (requests then hard-fail), OpenAI ≥6 months for GA models. Today a retired or renamed model id means silently failing detection jobs plus NULL-cost accounting. No reference OSS product surfaces this well — for a product whose value is unattended background LLM jobs, it is part of the compatibility promise.

What

• (The error classification + operator alert land in feat(server): instance-wide AI stop and daily spend alarm #1367 as a Gate-1 slice; this issue builds on them.)
• Admin-visible banner on the AI-settings page: "configured model X is deprecated/retired" + operator alert via feat(server): operator alerting for silent failures #1369.
• Reliability badges pinned to that model id flip stale automatically (feat(server,webapp): per-practice resolved-audit support summaries #1366's staleness machinery).
• Docs page: what happens when a model retires; the migration play is re-running the evaluation suite (feat(server): replay detection over frozen historical inputs #1364/feat(server,webapp): per-practice resolved-audit support summaries #1366) against the replacement inside the notice window.

Dependencies

#1369 (alert channel). Builds on #1367 (which owns the classification + alert); this issue owns the admin-visible banner, badge staleness, and docs.

Part of #1354.

[FelixTJDietrich]

Consolidated (capacity pass 2026-07-16): the operationally critical part — distinct classification of provider model-not-found/deprecated errors + operator alert — is now an AC on #1367; the pricing/model update procedure is in #1371. The admin banner UI and docs page are deferred; re-open a slim issue post-1.0 if the alert alone proves insufficient.

[FelixTJDietrich]

Reopened (mission recentering 2026-07-16): quality-first supersedes the capacity fold. The alert/classification core stays in #1367; THIS issue owns the admin-visible banner, the badge-staleness tie-in (#1366), and the operator docs page — genuinely differentiating for an unattended-LLM product (no reference OSS product surfaces model retirement well). Sequencing: after #1367 and #1369.