fix(xlsx): exclude phonetic guide text from cell values

[y4ho0]

Summary

• exclude <rPh> phonetic-guide text from ordinary XLSX cell display values
• preserve direct shared-string text and rich-text runs
• keep the guide available separately through the existing format.phonetic readback

Fixes #343

Validation

Using the reporter's attached sample.xlsx:

officecli view sample.xlsx html
# Before: <td data-path="/Sheet1/A1">項目コウモク</td>
# After:  <td data-path="/Sheet1/A1">項目</td>

officecli view sample.xlsx text
# Before: A1=項目コウモク
# After:  A1=項目

officecli get sample.xlsx /Sheet1/A1 --json
# text: "項目"
# format.phonetic: "コウモク"

officecli validate sample.xlsx
# Validation passed: no errors found.

I also created a shared-string cell with two formatted runs (Hello bold, world italic). view text still returns Hello world, view html retains both formatted spans, and officecli validate passes.

Project build:

dotnet build src/officecli/officecli.csproj -c Release --no-restore
# Build succeeded (one pre-existing CS8602 warning in ExcelHandler.SheetShift.cs).

[goworm]

Merged — thanks, the diagnosis and the approach were both right (reading the direct <t> / <r><t> runs instead of InnerText, and keeping the guide on format.phonetic).

One note for completeness: the same CT_Rst.InnerText call existed in three more readers, so the leak survived your fix on those paths. I verified each and fixed them on top in b730b4dd:

• GetCellDisplayValue, inline-string branch — an <is> cell with <rPh> still returned 項目コウモク
• ResolveCellRawText (chart cache) — both the inline and shared-string branches, so furigana could land in chart series caches
• AddRuns rich-text conversion — it folded the guide into the run it preserves when converting a plain cell to runs, which corrupted stored content rather than just display

Since SharedStringItem and InlineString both derive from RstType, the rule now lives in one RstTextWithoutPhonetic helper that all four readers call, and your shared-string logic was consolidated onto it. Regression tests cover shared-string, inline-string and multi-run rich text.