fix(webui): allow native text selection in chat via xterm.js bypass (#25720)

The chat panel renders via xterm.js, and when the inner Hermes TUI
enables mouse-events mode (CSI ?1000h family — used for nav inside
Ink overlays/pickers) every drag/double-click/triple-click in the
canvas is consumed by the terminal instead of producing a native
text selection. The reporter (macOS, Brave) confirmed:

- click-and-drag selects nothing
- Cmd+C with no selection copies the entire visible buffer
- existing CSS overrides and event handlers at the document layer
  have no effect — the issue is at xterm.js's mouse layer, not the
  DOM

Fix: two xterm.js options the user can opt into without disabling
mouse-events mode for the inner TUI:

- `macOptionClickForcesSelection: true` — holding Option (macOS)
  or Alt (Linux/Windows) during a click-and-drag bypasses mouse-events
  mode and produces a native xterm selection. This is the documented
  xterm.js path for this exact scenario. Selected text is copyable
  via Cmd+C / Ctrl+C through the existing OSC 52 + manual handlers.
- `rightClickSelectsWord: true` — right-click highlights the word
  under the pointer. Single-action path on top of the modifier-based
  bypass.

The two options coexist with the existing `macOptionIsMeta: true`
(which only affects keyboard, not mouse). No other code change
needed.

Fixes #25720.

web/src/pages/ChatPage.tsx

@@ -286,6 +286,17 @@ export default function ChatPage({ isActive = true }: { isActive?: boolean }) {
       fontWeight: "400",
       fontWeightBold: "700",
       macOptionIsMeta: true,
+      // Hold Option (Alt on Linux/Windows) to force native text selection
+      // even when the inner Hermes TUI has enabled xterm mouse-events
+      // mode (CSI ?1000h family). Without this, click-and-drag in the
+      // chat canvas selects nothing and Cmd+C falls back to copying the
+      // entire visible buffer, which is rarely what the user wants.
+      // See #25720.
+      macOptionClickForcesSelection: true,
+      // Right-click selects the word under the pointer. xterm.js default
+      // is false; enabling it gives users a single-action selection
+      // path on top of the modifier-based bypass above.
+      rightClickSelectsWord: true,
       // Single-scroll-system experiment:
       // let the inner Hermes TUI own transcript history/scroll behavior.
       // The outer browser xterm should act as a display/input bridge only.