fix(tui): default hyperlinks off for unknown terminals and tmux/screen

OSC 8 hyperlinks landed in #3248, but detectCapabilities() returned
hyperlinks: true in the unknown-terminal fallback. Terminals that
silently swallow OSC 8 (most xterm-compatible hosts, tmux/screen
without passthrough) end up dropping the URL from rendered markdown
links entirely, since the fallback 'text (url)' rendering is skipped
whenever hyperlinks is true.

- Unknown terminals now default to hyperlinks: false.
- tmux and screen (TMUX env, TERM starting with tmux/screen) force
  hyperlinks: false even when the outer terminal would otherwise
  advertise OSC 8 support. Image protocols also left disabled.
- Added detectCapabilities tests covering the known-capable set and
  the tmux/screen/unknown cases.

packages/tui/CHANGELOG.md

@@ -2,6 +2,14 @@
 
 ## [Unreleased]
 
+### Added
+
+- Added OSC 8 hyperlink rendering for markdown links when the terminal advertises support. Introduces a public `hyperlink(text, url)` helper and a `setCapabilities()` test override in `packages/tui` ([#3248](https://github.com/badlogic/pi-mono/pull/3248) by [@ofa1](https://github.com/ofa1)).
+
+### Changed
+
+- Tightened `detectCapabilities()` to default `hyperlinks: false` for unknown terminals and to force `hyperlinks: false` under tmux/screen (including nested sessions where the outer terminal would otherwise advertise OSC 8). Prevents markdown link URLs from disappearing on terminals that silently swallow OSC 8 sequences ([#3248](https://github.com/badlogic/pi-mono/pull/3248)).
+
 ## [0.67.5] - 2026-04-16
 
 ### Fixed