feat: add ZCode (Zhipu AI) platform support

[CNHLAIA]

Closes #329

Note: The platform count increases by 2 (14 → 16) because the previous Reasonix PR (#301) did not update the platform count or trellis-meta references; this PR brings both Reasonix and ZCode docs in sync.

Summary

Add ZCode (Zhipu AI's coding tool) as the 16th supported platform. ZCode is a class-2 (pull-based) platform — it uses agent files with context-reading prelude instructions instead of hooks.

Changes

Code (8 files)

File	Change
packages/cli/src/types/ai-tools.ts	Add zcode to union types and AI_TOOLS registry
packages/cli/src/configurators/zcode.ts	New: ZCode configurator (shared skills + commands + agents)
packages/cli/src/configurators/index.ts	Register ZCode in PLATFORM_FUNCTIONS
packages/cli/src/cli/index.ts	Add --zcode CLI flag
packages/cli/src/commands/init.ts	Add zcode to InitOptions
packages/cli/src/templates/zcode/index.ts	New: template entry with getAllAgents()
packages/cli/src/templates/zcode/agents/trellis-implement.md	New: implement agent with pull-based prelude
packages/cli/src/templates/zcode/agents/trellis-check.md	New: check agent with pull-based prelude

Documentation (12 files)

File	Change
README.md	Platform count 14 -> 16
README_CN.md	Platform count 14 -> 16
trellis-meta/references/platform-files/platform-map.md	Add Reasonix + ZCode rows
trellis-meta/references/platform-files/overview.md	Add .reasonix/ .zcode/ to directory list
trellis-meta/references/platform-files/agents.md	Add Reasonix + ZCode path rows
trellis-meta/references/platform-files/skills-and-commands.md	Add Reasonix + ZCode path rows
trellis-meta/references/platform-files/hooks-and-settings.md	Add pull-based platform note
trellis-meta/references/local-architecture/overview.md	Add directories
trellis-meta/references/local-architecture/generated-files.md	Add agent/command example paths
trellis-meta/references/customize-local/overview.md	Add .zcode/ to directory lists
trellis-meta/references/customize-local/change-agents.md	Add Reasonix + ZCode path rows
trellis-meta/references/customize-local/change-skills-or-commands.md	Add ZCode path row

Integration Pattern

ZCode follows the same class-2 pattern as OpenCode, Gemini CLI, and Reasonix:

• resolveAllAsSkillsNeutral for shared .agents/skills/ (byte-identical across platforms)
• applyPullBasedPreludeMarkdown for agent context loading
• Three output paths: .agents/skills/, .zcode/commands/trellis/, .zcode/cli/agents/

Validation

• pnpm typecheck — passed
• pnpm lint — passed
• pnpm test — 1023 passed (27 pre-existing failures unrelated to this PR)
• Manual testing on separate machine — all three output paths verified
• ZCode recognizes generated commands and agents