/talk renders code with highlighting and copy, and tables, as it streams, without jumping #8816

Follows #8752 (pull #8755 shipped copy, who and when, stick-to-bottom and the jump button, tool cards with Confirm and Cancel). Keep src/web/pages/talk.ts's server-drawn history and streaming, a small script, no React, and #8719's quiet rules.

Done looks like:

• [x] Code blocks are highlighted with the forge's existing highlighter, each with Copy. Tables and links render. An unfinished block while streaming does not reflow what is above it.
• [x] All markdown is rendered escaped. A test feeds <script> in text, in code and in a table cell.
• [x] The page's byte budget is held by a test.

Files: src/web/pages/talk.ts, src/web/pages/talk_client.ts, src/text/ (markdown), test/talk-page.test.ts

Reviewed pull #8834 at its head: ticked Code blocks are highlighted with the forge's existing highlighter, each with Copy. Tables and links render. An unfinished block while streaming does not reflow what is above it.; All markdown is rendered escaped. A test feeds <script> in text, in code and in a table cell.; The page's byte budget is held by a test..