skills(lark-im): card style guide's metric-card example sets `corner_radius` on `column` — real send fails with 200621 "unknown property"

What happened

The card style guide skills/lark-im/references/card/lark-im-card-style.md section 3 (指标卡模式, line ~134 on main) tells the model this pattern is mandatory whenever the content contains KPI/numeric words, and its example JSON (lines ~143-158) sets "corner_radius": "8px" directly on a column inside a column_set:

{
  "tag": "column_set",
  "flex_mode": "none",
  "horizontal_spacing": "12px",
  "columns": [
    { "tag": "column", "width": "weighted", "weight": 1,
      "background_style": "grey-50", "corner_radius": "8px",
      "padding": "12px", "vertical_spacing": "2px",
      ...

column does not support corner_radius in card 2.0 — the component reference in the same skill (components/column_set.md, "column 字段" table) lists background_style/padding/margin/etc. for column but no corner_radius. Any card built by faithfully following the style guide's example is rejected by the open platform at send time:

Lark API error: Failed to create card content, ext=ErrCode: 200621;
ErrMsg: msg: [parse card json err, please check whether the card json is correct],
value: [unknown property, property: corner_radius,
path: ROOT -> body -> elements -> [1](tag: column_set) -> columns -> [0](tag: column)],
code: 200621; (code: 230099)

Why it matters

This is an agent-facing skill doc: models follow the example verbatim, and the style guide marks the metric-card pattern as mandatory for numeric content, so any KPI/statistics card generated from these docs fails to deliver. The error only surfaces at send time, after authoring.

Reproduce

1. Take the metric-card example from section 3 of lark-im-card-style.md as-is (a complete card with that column_set in body.elements).
2. Send it via im/v1/messages with msg_type=interactive (or lark-cli im +messages-send).
3. The API returns code 230099 / ErrCode 200621 unknown property: corner_radius at the column path.

Removing "corner_radius": "8px" from the column makes the same card deliver successfully.

Suggested fix

• Remove corner_radius from the column in the section-3 example (keep background_style/padding/vertical_spacing, which are valid).
• Optionally add a warning line to the style guide: column does not support corner_radius; when rounded corners are needed, wrap the block in an interactive_container (section 4's pattern), which does support it.

Observed with the skill docs shipped in 1.0.64; the example is unchanged on current main.

Open skills/lark-im/references/card/lark-im-card-style.md and inspect section 3 alongside components/column_set.md, focusing on the metric-card JSON example and the column field table. Confirm the documented properties against the reported send error, then update the example so it matches the component reference and verify that the invalid corner_radius usage is no longer present.