fix(ui): render markdown tables

[alectimison-maker]

Summary

• Render GitHub-style Markdown pipe tables as semantic HTML tables in the chat sidepanel.
• Mirror the renderer and styles across Chrome and Firefox.
• Add regression and parity coverage for issue can't render tables #2838.

Motivation

Responses containing a header row, separator row, and pipe-delimited data rows were displayed as literal Markdown instead of a table. This is the user-visible failure reported in #2838.

Design

• Add a dependency-free table parser to the existing Markdown renderer.
• Run it after HTML escaping and after fenced/inline code extraction, so untrusted cell text remains escaped and pipes inside code do not alter table structure.
• Accept valid separator rows, escaped pipes, and ragged body rows while keeping ordinary pipe text unchanged.
• Add responsive overflow handling and readable header/cell borders without changing provider, storage, or browser APIs.

Testing

• node test/run.js — 1850 passed; 1 pre-existing failure for the missing tracked artifact dist/webbrain-chrome-32.1.0.zip in the Opera-safe license filename check.
• node --check src/chrome/src/ui/markdown-render.js && node --check src/chrome/src/ui/sidepanel.js && node --check src/firefox/src/ui/markdown-render.js && node --check src/firefox/src/ui/sidepanel.js — passed.
• npm run test:toolbar-guard — passed (33 tests).
• npm run test:security — passed (60/60 checks).
• Chrome unpacked extension check on sidepanel.html — passed; injected issue table rendered as one table with overflow-x: auto, and no page or console errors.

Firefox live browser verification was not available; Firefox parity is covered by the mirrored source and regression assertions.

Compatibility and risks

• No public API, provider, storage, or data migration changes.
• Fenced code blocks and inline code remain protected by the existing placeholder extraction.
• The parser intentionally targets chat sidepanel rendering; standalone skill-preview table rendering is deferred.

Scope

• Deferred support for tables in the separate skill-preview/history Markdown renderer.

Closes #2838

[vercel]

@alectimison-maker is attempting to deploy a commit to the esokullu's projects Team on Vercel.

A member of the Team first needs to authorize it.

[esokullu]

Review findings (fixed in 9e7f610)

Pushed follow-up commit 9e7f610f (fix(ui): keep markdown tables after headings and in history) to address the review on this PR.

P1 — Render tables before headings
renderMarkdownHeadings() swallows the trailing newline, so a table on the next line was glued onto the h2 and no longer matched as a table. formatMarkdown now runs renderMarkdownTables() first. A heading immediately followed by a pipe table renders as both an h2 and a <table>.

P2 — Persist tables as Markdown, not flattened cells
Assistant history is rebuilt with historyTextFromElement(), which treated TABLE/TR/TH/TD as blocks and stored one cell per line. Rendered tables (including .markdown-table-wrapper) now round-trip as pipe Markdown, keep inline markers such as **bold**, and escape | inside cells.

node test/run.js: 1851 passed. The remaining failure is the pre-existing Opera archive filename mismatch, unrelated to this change.