fix: emit hookSpecificOutput JSON on ZCode so rules reach the model

[Arteiimis]

Fixes #798

ZCode parses hook stdout as strict JSON and injects only additionalContext; the native-Claude raw-text output fails validation and is silently discarded, so the ponytail ruleset never reaches the model there. The hook itself runs fine — the state flag is written at session start — which is what makes the failure so quiet.

Changes

• Detect ZCode via ZCODE_APP_VERSION, which ZCode injects into every child process, hooks included. A Claude-compat variable alone (CLAUDE_PLUGIN_ROOT) can't distinguish the two.
• Reuse the Qoder hookSpecificOutput shape for ZCode in writeHookOutput. Unlike Qoder, ZCode has SessionStart, so ponytail-activate.js keeps handling startup injection — only the output shape differs from Claude Code.
• Same treatment for the off-mode early exit in ponytail-activate.js, where the bare OK text would also fail ZCode's strict JSON parse.
• Skip the statusline nudge on ZCode: its statusline configuration story is unverified, and the nudge points the agent at Claude's settings.json.
• No SubagentStart change: ZCode drops that event at registration time, which is already the desired behavior there.
• Tests mirror the Qoder block in tests/hooks.test.js: SessionStart injection, mode switch, deactivation.

Verification

• node --test tests/hooks.test.js and tests/hooks-windows.test.js pass; scripts/check-rule-copies.js and scripts/check-versions.js pass.
• Output shape follows ZCode's documented hook contract (strict-JSON stdout, hookSpecificOutput.hookEventName + additionalContext, cf. ZCode: SessionStart rules never injected — raw-text stdout fails ZCode's JSON validation #798 diagnostics: an event-specific output naming the wrong event fails validation).
• End-to-end injection on a live ZCode 3.10.2 session: reported in a follow-up comment once confirmed (the patch is running on the reporter's install).

[Arteiimis]

Verified end-to-end on the reporter's install (ZCode 3.10.2, Windows 11, ponytail 4.9.0 with this patch applied to the installed plugin): on a fresh session the SessionStart hook fires and the full ruleset reaches the model as injected additionalContext — no manual /ponytail needed. The UserPromptSubmit path (/ponytail mode switch) delivers its confirmation through the same envelope correctly.