fix(ui): stop the English admin models header from asserting a currency

[argszero]

Summary

The English column headers in the admin model management table read Input $ / Output $. The values rendered underneath are each model's price in its own currency — renderAdminModels() prints m.input_per_m / m.output_per_m raw, unconverted, in raw units — and the table marks the currency nowhere. config/config.toml ships a mixed catalog (10 CNY + 4 USD models), so the $ was simply wrong for the CNY rows: deepseek-v4-flash rendered as 1.5 under an Input $ header is not 1.5 dollars.

It was wrong from the day it was added: git log -S'"Input $"' → 98a7a9b (PR #97, the commit that introduced this table), whose data/models.example.json already carried 3 CNY vs 7 USD models.

The Chinese source text — admin.models.col.in/out = 输入价 / 输出价, and the prototype header — asserts no currency. The $ exists only in the English translation of the header (it is the only currency symbol in the whole 775-key pack), so this is a translation-introduced defect rather than a currency-modelling one: the fix is to stop asserting a currency, not to change how currencies are stored.

Scope: English values only, 2 keys, wording aligned with the sibling form labels (admin.models.form.in/out = Input price (/M tokens)). No key added or removed, no code changed, and the zh pack is byte-identical (md5 ef2d416b550a47dd97f5f1dbb319bb32 before and after).

Related Issue

Changes

• admin.models.col.in: Input $ → Input price
• admin.models.col.out: Output $ → Output price
• cache-bust ?v=20260911-13 → ?v=20260911-14 in ui/index.html (5 refs)
• 涉及配置/数据结构的改动已同步示例文件 — N/A, this is a copy-only change

Tests

• cargo test 全部通过 — 148 passed / 0 failed
• cargo fmt --check 通过
• cargo clippy --all-targets 无新增 warning
• 新增/更新了单元测试（如适用）— N/A (no Rust code touched)

i18n gates (values read from the real module's pack objects, not parsed by regex):

gate	result
key parity	PASS — 775 == 775, zero keys only-in-zh / only-in-en
the 2 fixed values, EN	PASS — Input price / Output price, no $
ZH values untouched	PASS — 输入价 / 输出价
currency symbols anywhere in the EN pack	PASS — 0
placeholder mismatches	PASS — 0

Runtime A/B (both trees built by one generator; baseline = git show HEAD:ui/..., fixed = work tree; cache-bust neutralized so it is not a variable). Rendered the admin models table in a headless browser against a stub /api/admin/models carrying one CNY and one USD model:

	EN baseline	EN fixed
headers	Provider, Model, **Input $, Output $**, Context, …	Provider, Model, **Input price, Output price**, Context, …
rows	deepseek-v4-flash 1.5 4.5 / gpt-5.6-sol 5 30	identical

• negative control: $ is asserted present in the EN baseline, so "gone after" is not vacuous
• ZH regression control: ZH headers (输入价 / 输出价) and both ZH data rows are byte-identical across trees — only the EN pack moved
• row control: all data rows byte-identical across trees — only the two header cells changed

Checklist

• 分支命名符合约定（fix/admin-models-currency-header）
• Commit message 使用 Conventional Commits 格式
• 单一职责，改动最小化（2 个 EN 值 + 1 处 cache-bust）