Fix terminal startup command echo race

[Jinwoo-H]

Summary

• increase the post-shell-ready startup command delay for daemon and local PTY paths
• add a regression guard for the early prompt echo race window
• keep timing tests tied to exported constants instead of duplicated literals

Repro

Before the patch, running:

orca terminal create --command "echo ORCA_ECHO_REPRO"

executed the command correctly, but rendered the typed line with the first character duplicated at the prompt, e.g. eecho ORCA_ECHO_REPRO. The same race made claude appear as cclaude/tclaude when launched through orca terminal create --command.

Verification

• pnpm exec vitest run src/main/daemon/post-ready-flush-gate.test.ts src/main/daemon/session.test.ts src/main/providers/local-pty-shell-ready.test.ts
• pnpm run typecheck:node

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