Docs: xlsx SKILL.md never mentions `add --from` (row/column cloning) — agents re-specify formatting cell by cell

## What's missing

The xlsx SKILL.md never mentions `add --from` (row/column cloning). Grepping the three shipped skills for `--from` returns **0 hits** in all of them.

That command is the one-liner answer to the most common editing task there is: *append a row to a sheet that already has formatting*. Without it, an agent's only path is to re-specify every cell property by hand, which is where it goes wrong.

Related: the "Reading & Analysis" section teaches `view outline` / `view text` as the way to orient in an existing file. Neither returns any formatting, so an agent that follows the skill faithfully never has the source formatting in context when it writes the edit.

## Why it matters

Observed with `sonnet-5` on v1.0.146. An agent was asked to add four rows to an existing formatted worksheet. It ran `view outline && view text` (as the skill instructs), got values only, and wrote a `batch` of `set --prop value=` calls. The new rows landed with no font, no borders, no alignment.

When told the formatting was missing, it recovered by reading `get "" --json` and emitting per-cell property batches — but it only covered **18 of the 36 cells** and reported the task complete, because `validate` passed. A second correction round was needed for the remaining rows.

With `add --from` in the skill, none of that happens: it is one call and the formatting is carried by the CLI.

## Reproduction

Formatting is not inherited without `--from`. This part is expected — `add` is documented as structural-only — it just isn't discoverable from the skill:

```bash
officecli create repro.xlsx
officecli set repro.xlsx /Sheet1/A1 --prop value=row1 --prop bold=true \
--prop border.left=thin --prop border.bottom=thin --prop alignment.horizontal=center
officecli set repro.xlsx /Sheet1/A2 --prop value=row2 --prop bold=true \
--prop border.left=thin --prop border.bottom=thin --prop alignment.horizontal=center

officecli add repro.xlsx /Sheet1 --type row --after "/Sheet1/row[1]" --prop cols=1 --prop c1=inserted
officecli get repro.xlsx "/Sheet1/A1:A3" --json
```

```
/Sheet1/A1 text='row1' format={type, font.bold, font.size, font.name, border.left, border.bottom, alignment.horizontal}
/Sheet1/A2 text='inserted' format={type} <-- bare
/Sheet1/A3 text='row2' format={type, font.bold, ...}
```

`add --from` does exactly the right thing, and this is what the skill should be teaching:

```bash
officecli add repro2.xlsx /Sheet1 --type row --from "/Sheet1/row[2]" --after "/Sheet1/row[2]"
officecli get repro2.xlsx "/Sheet1/A1:A3" --json
```

```
/Sheet1/A3 text='row2' format={font.bold, font.size, font.name, border.left, border.bottom, alignment.horizontal, numFmtId, numberformat} <-- all 8 carried
```

## Suggested fix

Two additions to `skills/officecli-xlsx/SKILL.md`:

1. **A row/column cloning recipe** under "Creating & Editing" — `add --type row --from "/Sheet1/row[K]" --after "/Sheet1/row[K]"`, framed as the default way to extend an existing formatted table, with the "add is structural-only, formatting props are Set-only" asymmetry stated next to it. `remove "/Sheet1/row[N]"` deserves a line in the same place; the skill currently shows `remove` only for charts and sheets, so agents blank cell values instead of deleting rows and leave a gap behind.

2. **A line in the editing workflow** noting that `view outline` / `view text` return values only, and that `get --json` (or `dump`) is what you run before editing a file whose look must be preserved. The existing "Preserve existing templates" bullet states the goal but not the procedure.

Scope note: `--from` exists for xlsx `row` and `column`. `docx add paragraph|table` and `pptx add slide|shape` do not advertise it, so this is an xlsx-skill issue only.

Verified on v1.0.146 (`officecli-mac-arm64`, sha256 `fdad1c51…3161`).

Open skills/officecli-xlsx/SKILL.md and inspect the Creating & Editing and editing-workflow sections, then compare their existing add and remove examples. Run the documented xlsx commands around add --from and get or dump to verify the examples; done means the skill explains row/column cloning, structural-only add behavior, row removal, and how to inspect formatting before edits.

Written by the indexing model from the issue text.