fix(projects): verify command echo before Enter; retry when shell startup swallows keystrokes

[milehimikey]

Problem

When a project's startup command is typed into a freshly created pane, the shell's startup can swallow keystrokes — most often just the first character, so claude runs as laude ("command not found"). Two weaknesses in runCommand combine to cause this:

• waitForPaneReady returns on the first non-blank read. Shells with slower startup (compinit, plugin managers, prompt frameworks) paint output in bursts before the line editor accepts input, so typing starts too early and characters land in the gap.
• After typing, the echo check (waitForPaneText) has no teeth: when it times out, Enter is pressed anyway, submitting the mangled line.

Fix

• waitForPaneReady now waits for quiescence — two consecutive identical non-blank reads 200ms apart — instead of first paint (call-site timeout 5s → 10s).
• waitForPaneText reports whether the probe appeared.
• runCommand only presses Enter once the command visibly echoes back intact. On a failed echo check it clears the line (ctrl+u — backward-kill-line in both zsh emacs and vi-insert keymaps) and retypes, up to 3 attempts, before degrading to the previous blind-Enter behavior so a shell that never echoes (or a full-screen program) still works.

Happy path cost is one extra 200ms quiescence read; the retry path only engages when the echo check fails.

Testing

• go test -race ./... passes.
• Reproduced the original failure with a slow-starting zsh (oh-my-zsh + compinit + mise + vi-mode) where project launches reliably typed laude; with this change the command lands intact across repeated launches, including with an artificial sleep 2 at the top of .zshrc.

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