Roam: Convert {{[[table]]}} blocks to Markdown pipe tables

[cristip73]

Summary

Roam Research {{[[table]]}} blocks are currently not converted during
import — the table marker text is left as-is (the only handling was a
commented-out replaceAll at line 289), and table children become plain
bullet lists that lose all tabular structure in Obsidian.

This PR adds proper structural conversion of Roam tables into standard
Markdown pipe tables.

Partially addresses #180.

How it works

• A new regex roamTableRe detects {{[[table]]}} and {{table}}
  markers (case-insensitive)
• In jsonToMarkdown(), when a table block is detected, processing is
  delegated to a new convertRoamTable() method instead of the normal
  bullet/children recursion
• convertRoamTable() walks each row's linear first-child chain to
  extract columns (Roam encodes table cells as nested first-children),
  scrubs Roam markup via the existing roamMarkupScrubber(), escapes
  pipe characters, pads uneven rows, and builds a standard pipe table

Edge cases handled

• No children → empty output (table marker removed cleanly)
• Uneven row lengths → padded with empty cells
• Pipes in cell content → escaped as \|
• Deep nesting (4+ columns) → linear chain walk handles any depth
• Roam markup in cells → links, TODOs, highlights, dates all converted
• Table inside nested outline → indent preserved on all table lines

Test plan

• Build passes (npm run build)
• Lint passes (npm run lint)
• Import a Roam JSON export containing {{[[table]]}} blocks and
  verify pipe tables render correctly in Obsidian
• Verify non-table blocks are unaffected

🤖 Generated with Claude Code

[tgrosinger]

Thank you for submitting this improvement! Overall it looks great, just a few suggestions.

I also noticed when running the tests/roam/small-test-graph.json, the table is still indented under the bullet point, causing it to not render correctly. Can that be fixed here too?

[tgrosinger]

The current regex has two independent optional groups:

/^\{\{(\[\[)?table(\]\])?\}\}$/i
       ^^^^        ^^^^
       group 1     group 2

Each ? makes its group independently optional, producing 4 possible matches:

Group 1	Group 2	Matches	Valid Roam?
absent	absent	{{table}}	yes
present	present	{{[[table]]}}	yes
present	absent	{{[[table}}	no
absent	present	{{table]]}}	no

The proposed fix ties the brackets together as a single alternation:

/^\{\{(\[\[table\]\]|table)\}\}$/i

This only matches {{[[table]]}} or {{table}} -- brackets are always balanced.

Suggested change

	const roamTableRe = /^\{\{(\[\[)?table(\]\])?\}\}$/i;
	const roamTableRe = /^\{\{(\[\[table\]\]|table)\}\}$/i;

[tgrosinger]

If a Roam table cell has multiple children (e.g., user added sub-items), all but the first are silently discarded with no warning. This could cause data loss without any indication to the user. Consider logging a warning when current.children.length > 1.

[tgrosinger]

• children: [] (truthy) enters convertRoamTable, returns '' -- table marker vanishes silently
• children: undefined falls to the else branch and renders raw {{[[table]]}} in output

Consider having the table-detection guard not require json.children, and letting convertRoamTable handle all cases uniformly.

[tgrosinger]

The formatting of the various table sections could be unified and simplified by inserting the separator row after the header:

const separator = tableData[0].map(() => '---');
tableData.splice(1, 0, separator);

const lines = tableData.map(row => indent + '| ' + row.join(' | ') + ' |');