feat: add hover controls to add/remove table rows and columns

[netqo]

Closes #30

Problem

Editing a table in the live editor was awkward. Rows could only be added by
pressing Enter/Tab inside a cell, and there was no way at all to add or remove a
column from the UI: the column mutation primitive (_tableColumnResult) already
existed in writemark.js but had no caller.

What this does

Adds hover-revealed controls on live-editor tables:

• a + tab at the top-right adds a column, and a + tab below the table adds a
  row;
• a - tab centered above each column deletes that column, and a - tab at each
  body row's right edge deletes that row.

All four are identically sized, slightly-rounded tabs (2px corners, matching the
Publish button) and appear only while hovering the table (each delete tab shows
when hovering its column/row).

How

• The controls are rendered as part of the table markup, so they are recreated
  on every re-render and never touch the markdown source: they are
  contenteditable="false", carry no data-editable/data-from, and are
  ignored by the DOM-to-source mapping.
• Positioning uses no JavaScript measurement: each tab is centered on a real
  table edge via CSS (top, bottom, or right). The block adds no padding, so the
  table keeps its normal spacing and stays flush with the editor, and every tab
  stays within the table box - nothing spills outside to get clipped or to
  trigger a scrollbar.
• Clicks are routed through the existing delegated live-click handler to the
  existing row/column primitives (_tableColumnResult,
  _tableRowInsertionResult, _tableDeleteRowResult), so undo/redo and
  screen-reader announcements work unchanged.
• Controls are hidden when the editor is read-only or disabled; the delete-column
  tab is hidden while only two columns remain and the delete-row tab while only
  one row remains, keeping two columns and one row as the minimums.

No changes to the Rust renderer or the published output - this is editor-only.

Scope

One file, templates/writemark.js (+72 / -5): the _renderTable markup, a small
CSS block, two lines in the live-click handler, a one-line mousedown guard, and
an ~18-line dispatch method.

Testing

• Functional: a jsdom harness inserts a table, dispatches real clicks on each
  control, and asserts the markdown source mutates correctly (add-col, add-row,
  del-col, del-row), that a single-column table hides the delete-column tab, and
  that a read-only editor renders no controls. 9/9 passing.
• Verified in the running app that the editor JS is served intact (the inline
  build strips module exports and line comments; both the raw module and the
  stripped inline form parse), and that tables behave as described.

[du82]

There's unnecessary and unexpected horizontal margins on the tables now. The space in pink shouldn't exist and the tables should be flush with the edges:

There's no option to remove a column:

[du82]

Ignore my second critique, turns out I was doing it wrong! Fix padding and should be good to go

[netqo]

okie one sec

[du82]

Much better solution! One issue I see is it doesn't make sense to have a one-column table, and it causes a breakage anyways. I propose not showing the option to remove a column if there's only two:

[netqo]

makes sense also did the same for when theres only 1 row in the table.

[du82]

LGTM!

[du82]

Send a Monero sub-address if you'd like to claim a bounty

[netqo]

yay okie
86kQY5HoqFDghmSefmWicf8vx7x5xSWVF6svismyy9wBd58zRrHxrmfQRxdzTE1d3eLbpRC5pVb5j9g8PL8vN3mp5skyVEy

[du82]

Please contact me on Signal regarding the bounty. It's important.