feat: integrate pi as a first-class agent / pi 作为内置 Agent 接入

[Rladmsrl]

What

Integrate the pi CLI coding agent (@earendil-works/pi-coding-agent) as a first-class agent in Glint, alongside Claude / Codex / OMP / Grok.

Why

pi is a node-based CLI agent with its own TypeScript extension API. Like OMP/Grok, it exposes lifecycle events through extensions rather than shell hooks, so it needs the same "drop a TS extension + auto-discover" treatment as the other TS-based agents.

How

• PiHookInstaller — drops a TS extension (glint-agent-bridge.ts) into ~/.pi/agent/extensions/ (pi's global auto-discovery dir). The extension forwards pi lifecycle events → Glint's Unix socket:
  • session_start / agent_start / agent_end / agent_settled → idle/thinking
  • tool_call / tool_result → running/thinking
  • session_before_compact → compacting
  • ask_user_question / exit_plan_mode tool calls → needsReply
  • Only fires when Glint's pane env vars are present → a pi session outside Glint is a no-op.
• PaneAgentKind.pi — new case wired through the enum, iconKind mapping, session restore command (pi --session-id <id>, falls back to pi --continue), and agentKind(named:) matcher using exact "pi" string match (avoids false-positives on pipe / pip / copy).
• WorkspaceStore — piHooksInstalled published state, install/uninstall methods, auto-install spec, restorePiSession toggle.
• SettingsView — new Pi SettingsCard with install/uninstall controls + status pill.
• Localizable.xcstrings — new UI strings localized for en + zh-Hans.

Checklist

• PaneAgentKind.pi case added to all exhaustive switches
• PiHookInstaller follows the same pattern as OmpHookInstaller / GrokHookInstaller
• Exact-match process name detection (no substring contains)
• New UI strings localized in en + zh-Hans
• Builds clean under Xcode-beta (will verify in CI)