Clickable links, full-width terminal and exact page history

- OSC 8 hyperlinks and plain URLs are clickable on the screen and in the
  page history. Links to a section of the current page scroll there,
  others open in a new tab. Links show their target on hover and invert
  in their own color, like the page's links.
- The terminal fills the page column (the fit addon kept room for a
  hidden scrollbar).
- Lines in the page history sit exactly on the terminal's cell grid,
  also for wide and fallback-font characters, and no longer wrap.
- The first command is sent as soon as the shell's line editor is ready,
  instead of guessing from a pause in its output.

Co-Authored-By: Claude Opus 5.5 (1M context) <noreply@anthropic.com>

package.json

@@ -11,7 +11,7 @@
     "@noble/ciphers": "^2.4.0",
     "@noble/curves": "^2.4.0",
     "@noble/hashes": "^2.4.0",
-    "@xterm/addon-fit": "^0.11.0",
+    "@xterm/addon-web-links": "^0.12.0",
     "@xterm/xterm": "^6.0.0",
     "astro": "^7.4.2"
   }