fix(docx): float an anchored drawing, and draw a table's own borders

[andiwand]

🤖 Generated with Claude Code

Closes #803.

What was wrong

Two defects a user reported from a German letterhead + invoice, both docx-only. The html renderer already implements the whole anchor/wrap matrix and odf feeds it properly; it is the docx adapter that starved it.

A wp:anchor drawing rendered inline. frame_anchor_type returned AnchorType::as_char unconditionally, frame_x/frame_y returned nullopt, and frame_style returned {} — so a floating logo was laid out at its anchor's character position, landing between two lines instead of below them.

A table's own borders were dropped. resolve_table_cell_style_ read w:tcPr/w:tcBorders only. Nothing read w:tblPr/w:tblBorders, so a table stating its rules once — directly or through a w:tblStyle — rendered borderless. And w:sz was read as half-points where [ECMA-376] 17.3.4 says eighths, so every border that did draw was four times too thick.

The change

• wp:anchor reports its real anchor type, its wp:positionH/wp:positionV offset (read_emus_text), and a GraphicStyle carrying its wrap and its side. A page-relative offset is dropped rather than measured against the wrong box.
• table_cell_border resolves each cell's edges: its own w:tcBorders over the neighbour's over the table's, and only the edges the cell leads, so a rule between two cells is one line. New TableStyle::border, ::border_inside_horizontal, ::border_inside_vertical, mirrored in the JNI, Apple and Python bindings.
• read_border_node reads w:sz in eighths of a point, and w:val="none"/"nil" now says no border rather than saying nothing.
• td{vertical-align:top} in document.css — word and odf start a cell's content at the top where the browser default centres it; a sheet still says its own.
• A right-floated frame with no offset no longer gets margin-right:calc(100% - 0 - width), which pinned it to the left.

Verified

New fixture docx/float-drawing+table-borders.docx — a wp:anchor wrapped top-and-bottom at an offset, a table whose borders live on a w:tblStyle, and a cell whose w:tcBorders override them. 272 lines of unit tests over the border resolution.

Full suite 1417 passed / 6 pre-existing skips. Reference output regenerated: 14 public and 7 private files, every one a table gaining the borders it states, plus image-anchor.docx, where two stacked images now sit side by side at their own offsets — which is where LibreOffice puts them too. The three odt files lose the redundant margin-right; nothing there moves by more than a pixel. Changed TUs re-checked under -Werror.