docs(byteplus): warn that byteplus is per-token, not Coding Plan (#80)

* docs(byteplus): warn that `byteplus` is per-token, not Coding Plan

Self-followup on PR #78. The BytePlus official docs explicitly warn:

  Do not use the standard model endpoint
  (https://ark.ap-southeast.bytepluses.com/api/v3) [for Coding Plan
  workloads], as requests there bypass Coding Plan quota and incur
  separate charges.
  — https://docs.byteplus.com/en/docs/ModelArk/1928261

Without this warning visible to users, anyone with a Coding Plan
subscription who picks `provider = "byteplus"` will silently bill
against their per-token USD balance instead of consuming the
subscription quota they paid for.

Adds a prominent "BILLING — READ BEFORE USE" block to byteplus.toml
making the per-token vs subscription split unambiguous, and a
companion note in byteplus-coding.toml pointing back so the choice is
discoverable from either side. Also calls out which capabilities are
unique to the standard endpoint (image / video) so the choice isn't
"just use Coding Plan for everything".

No model definitions or pricing changed.

* chore(byteplus): drop superseded model entries (21 → 11) (#81)

The original byteplus.toml from PR #78 enumerated every BytePlus
ModelArk endpoint that returned HTTP 200, regardless of whether a
sane user would still pick it. Trims to the current per-family
flagship plus useful fast/preview tiers.

Removed (10):
  Text:
    seed-2-0-lite-260228       — superseded by seed-2-0-mini in the
                                 fast/cheap niche
    seed-1-8-251228            — superseded by seed-2-0 family
    seed-translation-250915    — too narrow; chat models cover this
    deepseek-v3-1-250821       — superseded by deepseek-v3-2
  Image:
    seedream-3-0-t2i-250415    — superseded by seedream-4-5 / 5-0-lite
    seedream-4-0-250828        — same
  Video:
    seedance-1-0-lite-i2v-250428    — superseded by 1-5 / dreamina-2-0
    seedance-1-0-lite-t2v-250428    — same
    seedance-1-0-pro-250528         — same
    seedance-1-0-pro-fast-251015    — same

Kept (11):
  Text (6):  seed-2-0-pro/mini/code-preview, glm-4-7,
             deepseek-v3-2, gpt-oss-120b
  Image (2): seedream-4-5, seedream-5-0 (lite)
  Video (3): seedance-1-5-pro, dreamina-seedance-2-0,
             dreamina-seedance-2-0-fast

Also corrects two per-piece / per-K price comments that the trim
left orphaned over the wrong [[models]] block (4-5 = $0.0400, not
$0.0300; 1-5-pro = $0.0024/$0.0012 with/without audio, not
$0.0018/K) and updates the header capability list to match the
new model set.

providers/byteplus-coding.toml

@@ -2,10 +2,21 @@
 # International edition's Claude Code-compatible endpoint with friendly model aliases.
 # Models: 9 (auto-routed alias + 8 named models)
 #
-# Pricing matches the underlying versioned snapshots in byteplus.toml. The
-# Coding Plan endpoint exposes friendly stable names that route to the
-# current production snapshot, so versions advance silently without config
-# changes (use `ark-code-latest` to always get the best current routing).
+# 💡 BILLING — calls here count against your **Coding Plan
+# subscription quota**, not your per-token ModelArk USD balance. If you
+# don't have a Coding Plan or want per-token billing instead, use the
+# `byteplus` provider in byteplus.toml. The Coding Plan endpoint also
+# does not expose image / video / embedding models — only the text
+# models listed below.
+#
+# Pricing fields below mirror the underlying versioned snapshots in
+# byteplus.toml for catalog accounting purposes; actual subscription
+# consumption is tracked by the BytePlus console, not these numbers.
+#
+# The Coding Plan endpoint exposes friendly stable names that route to
+# the current production snapshot, so versions advance silently without
+# config changes (use `ark-code-latest` to always get the best current
+# routing).
 
 [provider]
 id = "byteplus_coding"