Add aict each: batch tool for piping find/grep results into another tool

[github-actions]

Description

AI agents frequently need to apply one tool to many paths — e.g., stat every file returned by find. Currently this requires spawning a separate process per file. Add aict each <tool> [flags] which reads newline-separated paths from stdin and runs the given tool on each, collecting all results under a single root element.

Usage

# stat every Go file in the project
aict find . -name "*.go" --plain | aict each stat

# checksum every file found
aict find . -type f --plain | aict each checksums

Proposed XML Output

<each tool="stat" count="42" timestamp="1746123456">
  <stat path="main.go" ...> ... </stat>
  <stat path="utils.go" ...> ... </stat>
</each>

Implementation Notes

• Read stdin line by line
• For each path, call the registered tool function directly (not via exec)
• Collect results into a wrapper element
• Support --workers N for parallel execution
• Empty stdin should produce valid XML with count="0"

Related

• internal/tool/tool.go registry
• Phase 4 in ROADMAP.md