fix(coding-agent): pass OSC 52 through tmux

[chupe]

Problem

Remote clipboard writes emitted raw OSC 52. tmux could consume it without forwarding it through SSH, so /copy and fullscreen selection reported success while the workstation clipboard stayed unchanged.

Solution

Probe the effective #{allow-passthrough} value for the current pane. When enabled, wrap OSC 52 with the existing wrapTmuxPassthrough() helper. Keep raw OSC 52 outside tmux and when passthrough is disabled or unavailable, preserving the set-clipboard on path.

Testing

• npm --prefix packages/coding-agent test -- test/clipboard.test.ts (12/12)
• npm run check
• Senpi QA tmux TUI smoke (5/5)
• Real tmux passthrough-on transport to the outer client
• Real tmux passthrough-off fallback through set-clipboard on

Full npm test exceeded the 30-minute limit. The run also hit missing @earendil-works/pi-tui dist resolution under packages/ai in the no-lifecycle checkout.

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Summary by cubic

Passes OSC 52 clipboard writes through tmux's DCS passthrough so remote /copy and fullscreen selection actually reach the workstation clipboard instead of being swallowed by tmux.

Changes

• Probes #{allow-passthrough} and wraps the escape sequence with wrapTmuxPassthrough() when enabled.
• Falls back to raw OSC 52 outside tmux or when passthrough is disabled, preserving the set-clipboard on path.
• Replaces timer-based clipboard test waits with explicit native-write completion and adds passthrough-enabled and disabled remote tmux cases.

^{Written for commit 6fb3c13. Summary will update on new commits.}