fix(LinuxShellExecutor): fix RLIMIT_AS/NOFILE defaults causing Node.js V8 OOM

[XiaoHeiGe527]

Problem

When running shell commands via LinuxShellExecutor, the default resource limits cause Node.js child processes to crash with:

Fatal process out of memory: SegmentedTable::InitializeTable (subspace allocation)
Trace/breakpoint trap (core dumped)

Root cause: RLIMIT_AS=536870912 (512MB virtual address space) is set as the default. Node.js V8 with pointer compression requires ~4GB of virtual address space just to initialize.

Additionally, RLIMIT_NOFILE=64 (64 file descriptors) is too low for Node.js (system default ~1024).

Diagnosis

Confirmed with:

# OLD 512MB: Node.js crashes silently
ulimit -v 524288; node -e "console.log(42)"  # no output, killed

# With fix (0 = no limit): works
ulimit -t 30 -f 20480 -u 10; node -e "console.log(42)"  # 42

This caused false perception that plugins (LightMemo, PaperReader, RAGDiaryPlugin, UrlFetch) were dead. They work normally when spawned by VCP directly.

Changes

1. RLIMIT_AS default: 536870912 (512MB) → 0 (no restriction)
2. RLIMIT_NOFILE default: 64 → 0 (inherit system default ~1024)
3. -v and -n ulimit flags: now conditional — only emitted when limit > 0
4. plugin-manifest.json: clarify ; is blocked, guide AI to use && instead

Backward Compatibility

Users with explicit RLIMIT_AS/RLIMIT_NOFILE values in config.env are unaffected.

🤖 Generated with Claude Code