fix: prevent terminal container from overflowing page on desktop

The desktop terminal page sometimes grew an outer scrollbar because the
terminal instance/wrapper/container chain lacked height constraints.
Without min/max-height enforcement, xterm.js's internal viewport could
expand its parent flex/grid track past the available space.

- Add overflow: hidden to .terminal-page.
- Add max-height: 100% and overflow: hidden to .terminal-instance.
- Add max-height: 100% to .terminal-wrapper.
- Add min-height: 0 to .terminal-container.
- Constrain .xterm-viewport to max-height/width 100% so it fills but
  never exceeds its container.

Quality gates: npm run typecheck, npm run lint, npm test -- --run (87 passed).

Refs: openspec/changes/fix-terminal-container-overflow

apps/.pi-map.md

@@ -4,10 +4,10 @@ dir: apps
 index: apps/.pi-map.index.md
 
 ## role
-Container for independent, deployable application modules that compose the overall system.
+Contains the deployable application entry points and executable configurations for the project.
 ## files
 ## arch
-Monorepo-style multi-app structure where each sub-directory is a self-contained application sharing common infrastructure and dependencies.
+Modular application structure with separate, self-contained app modules that compose shared libraries into runnable binaries.
 ## tags
 -
 ## symbols