fix(opencode): sub-1% usage units (port 0.45.2 #2331)

[Finesssee]

Summary

First PR of the 0.43 → 0.45.2 Windows port stack.

Ports upstream CodexBar steipete#2331 / v0.45.2: OpenCode and OpenCode Go must not treat a computed used/limit percent (already 0…100) with the direct-field fraction heuristic (<= 1 → *100). That turned real 1% usage into 100% (false exhausted).

• Direct fields (usagePercent, etc.) may still be 0…1 fractions → scale to percent
• used/limit (and aliases) stay as (used/limit)*100 with no second scale
• Drop raw "usage" as a percent key in the scraper (token counts)

Audits (read-only upstream)

• %TEMP%\port-045\audit-backend.md
• %TEMP%\port-045\audit-ui.md
• %TEMP%\port-045\audit-skip.md

Test plan

• cargo test --manifest-path rust/Cargo.toml --lib providers::opencode
• cargo test --manifest-path rust/Cargo.toml --lib providers::opencodego
• New fixtures: used=1/limit=100 → 1%; used=1/limit=200 → 0.5%; direct 0.25 → 25%

No version bump / packaging (port stack continues).

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