feat(llm): odswiez modele i cennik - Claude 5, Gemini 3.7 Flash, GPT-5.6

[mjdch]

Summary

Refreshes which LLM models Patron offers and what they cost, replacing every
retired or mispriced entry in the model picker and the usage-panel pricing
table with live-catalog data, verified against the vendor pages and the
OpenRouter catalog on 2026-08-26.

Changes

Backend (backend/)

• lib/llm/models.ts: CLAUDE_MAIN/MID_MODELS -> Opus 5 / Sonnet 5 (4.x
  removed - same price, weaker model). OPENAI_MAIN/MID/LOW_MODELS -> the
  5.6 family (sol/terra/luna) replacing 5.4/5.5. GEMINI_MAIN_MODELS gains
  gemini-3.7-flash alongside the existing 3-flash-preview (kept because
  it's cheaper direct-from-Google; 3.7 is only cheaper on OpenRouter).
  DEFAULT_MAIN/TITLE/TABULAR_MODEL moved to openrouter/google/gemini-3.7-flash.
  New LEGACY_MODEL_ALIASES in resolveModel() so a lawyer's saved
  tabular_model on a retired id resolves to its successor instead of
  silently falling back to a different vendor's default.
• lib/llm/pricing.ts: PRICING rewritten keyed by the full model id
  (native and openrouter/... tracked separately) - the previous
  last-segment match never matched OpenRouter's dotted slugs against native
  dashed ids, so every OpenRouter-Anthropic model silently priced as
  "unpriced". Every rate re-sourced from the billing path that actually
  charges it (first-party for the own-key path, OpenRouter catalog for the
  openrouter/ path) rather than one catalog for everything. Retired
  models' price rows are kept (historical llm_route events still need
  pricing) and marked legacy in comments.
• Tests: per-model pricing coverage, an OpenRouter-mirror-exists check, a
  regression for the dotted-slug match, and three resolveModel alias
  tests. Fixed a stale openrouter.test.ts assertion that used the now-
  retired gpt-5.5 as its example of "a valid native id".

Frontend (frontend/)

• ModelToggle.tsx: picker entries updated to match (Opus 5 / Sonnet 5,
  Gemini 3.7 Flash added, GPT-5.6 sol/terra/luna), retired entries removed,
  DEFAULT_MODEL_ID synced to the new backend default.

Tooling (.claude/skills/)

• New upgrade-llm-models skill capturing this as a repeatable playbook:
  the four files that must stay in sync, the decision table (cheaper/same
  -> replace, pricier -> add alongside, no newer model -> leave alone,
  governance blocker -> don't ship), the per-billing-path pricing rule, and
  a bundled script that caches the OpenRouter catalog and prints per-MTok
  prices for one vendor.

Why

Two of the three vendors had a strictly-better replacement sitting unused:
Claude Opus 5 costs exactly what Opus 4.8 cost, and OpenAI's 5.6 family
undercuts 5.4/5.5 by a wide margin (e.g. gpt-5.4-mini $0.75/$4.50 ->
gpt-5.6-luna $0.20/$1.20 for the same role). Gemini had no such upgrade
(3.1 Pro is already current; the newer Flash generation is pricier at
Google's own rates), so it was handled differently - added alongside, not
swapped in, and the OpenRouter route to it was still cheaper so the default
moved there specifically.

No contract promised by the Constitution changes (no SSE event, MCP
citation format, or audit log payload touched).

Testing

• npm test --prefix backend - 1475 pass / 0 fail / 5 todo (was 1467)
• npx tsc --noEmit - backend clean
• npm test --prefix frontend - 43 pass / 0 fail
• npx tsc --noEmit - frontend clean
• Manually verified locally: started backend (sqlite/local mode) + frontend
  dev servers, confirmed /account/models compiles and serves 200 with no
  runtime errors in either dev log.

Governance / Constitution AI

• No contracts were broken (SSE events, MCP citations, audit_log).
• If a contract changed: ADR added under governance/adr/. (N/A - none changed)
• If a Constitution principle changed: version bumped in CONSTITUTION.md + changelog row. (N/A)

Tests

• npm test passes (1475/1475 backend, 43/43 frontend - both grew from baseline).
• No new lint warnings.
• tsc --noEmit clean on both backend and frontend.

License confirmation

By opening this PR I confirm my contribution is licensed under
AGPL-3.0-only (Patron shell). I followed the
DCO.