fix(pricing): drop the invented 200K premium for Claude 4.6+ models

Anthropic's pricing page ('Long context pricing') states that Claude
4.6 and later models include the full 1M token context window at
STANDARD pricing — a 900k-token request bills at the same per-token
rate as a 9k one. The hand-tracked override table wrongly extended the
pre-4.6 1M-beta premium to sonnet-4-6 and opus-4-6/4-7/4-8, silently
surcharging their >200K requests (verified live: +$19.97 on one
box's opus-4-8 usage vs ccusage's correct flat pricing).

The table now carries only claude-sonnet-4-5 — the one premium-era
model still served first-party (plain sonnet-4 is retired, and a bare
'claude-sonnet-4' row would token-prefix onto 4-6+ ids). Its rates
match the 1M-beta announcement and LiteLLM's above_200k data. Also
adds the claude-opus-5 fast multiplier (2x — the pricing page lists
fast mode at $10/$50 vs $5/$25), which both our table and
ccusage's embedded overrides were missing.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>