feat(web): accept K and M suffixes in the context window field

The catalog's context window is now a text field that reads a decimal K or M
suffix — 1M is 1000K, matching how model capacities are quoted — and stores
the plain token count, so settings.yaml and the adapter are unchanged.

A stored count reads back in the shortest form that round-trips: 1000000 as
1M, 256000 as 256K, and 131072 written out, because it is not a whole number
of thousands. The field holds the typed text while its row has focus, since
re-deriving it from the parsed count on every keystroke would rewrite 1000
to 1K mid-word; text that does not parse stays on screen so the save-time
rejection names a row the user can still see and correct.

apps/web/tests/snapshots/onboarding-deepseek-config/models.expected.md

@@ -14,7 +14,7 @@
   - paragraph: 填入各提供方的 API 密钥即可使用其模型。
   - list:
     - listitem:
-      - text: DeepSeek 已启用
+      - text: DeepSeek
       - button "编辑"
       - text: DeepSeek deepseek-official API 密钥
       - textbox "API 密钥":
@@ -36,7 +36,9 @@
           - textbox "显示名称 1":
             - /placeholder: 留空时使用模型 ID
             - text: DeepSeek-V4-Pro
-          - spinbutton "上下文窗口 1": "1000000"
+          - textbox "上下文窗口 1":
+            - /placeholder: 1M
+            - text: 1M
           - button "删除模型":
             - img
             - text: 删除模型
@@ -44,7 +46,9 @@
           - textbox "显示名称 2":
             - /placeholder: 留空时使用模型 ID
             - text: Private Preview
-          - spinbutton "上下文窗口 2": "131072"
+          - textbox "上下文窗口 2":
+            - /placeholder: 1M
+            - text: "131072"
           - button "删除模型":
             - img
             - text: 删除模型