feat(models): add Claude Fable 5.1 and correct Sonnet 5 pricing

Register `claude-fable-5-1` in the CLIProxy model catalog, the dashboard
catalog, and the usage pricing registry.

Pricing is taken from Anthropic's official pricing page:

- Fable 5.1 base rates are $10/$50 per MTok with a $12.50 5m cache write,
  matching Fable 5.
- Cache hits bill at 0.025x base input ($0.25/MTok) rather than the
  standard 0.1x multiplier. Anthropic applies that reduced rate only to
  Fable 5.1 and Mythos 5.1, so this entry cannot derive its cache rates
  from CACHE_READ_MULTIPLIER.

This also corrects Claude Sonnet 5 from $3/$15 to $2/$10 (cache write
$2.50, cache read $0.20). The launch introductory rate became the
standard price and the increase scheduled for 2026-09-01 was cancelled,
so the previous entry over-reported Sonnet 5 usage cost by 50%.

Thinking on Fable 5.1 is always on and can only be steered through
effort levels, so the catalog entry exposes the same `low`..`max` level
surface as Fable 5 and Opus 5 instead of a manual token budget.

The GitHub Copilot catalog is deliberately left unchanged, since Copilot
availability for Fable 5.1 is not verified; surfacing it there would
offer a model the backend may reject.

Regenerates docs/reports/hardening-inventory.{json,md} so the ci-parity
gate matches the source tree.

ui/tests/unit/ui/lib/preset-utils.test.ts

@@ -22,6 +22,7 @@ describe('claude preset utils', () => {
 
     expect(claudeCatalog.defaultModel).toBe('claude-sonnet-5');
     expect(ids).toContain('claude-sonnet-5');
+    expect(ids).toContain('claude-fable-5-1');
     expect(ids).toContain('claude-fable-5');
     expect(ids).toContain('claude-opus-5');
     expect(ids).toContain('claude-opus-4-8');