fileSuggestion: support structured output with display metadata (description/annotation)

Feature Request

Problem

The current fileSuggestion API only supports plain file paths as output (one per line). There's no way to display additional context alongside suggestions — such as last modified time, git diff stats, or custom descriptions — without that metadata being inserted into the input box when a suggestion is selected.

Current Behavior

# fileSuggestion script output (stdin → stdout)
src/lib/saveSessionMemory.ts
src/hooks/useSessionMemory.ts
docs/architecture/memory-system.md

Each line is treated as both the display text and the inserted value. Appending any metadata (e.g. src/foo.ts 2h ago +5/-3) causes Claude Code to treat the entire line as a file path, which fails.

Proposed Solution

Support a structured output format that separates display text from insert value, similar to VS Code's CompletionItem (label + detail + insertText).

Option A: Tab-separated format

src/lib/saveSessionMemory.ts\t2h ago  +12/-3
src/hooks/useSessionMemory.ts\t1d ago  +5/-0
docs/architecture/memory-system.md\t3d ago

• First field = file path (inserted on selection)
• Second field (after \t) = display-only annotation (shown but not inserted)
• Backward compatible: lines without tabs work as before

Option B: JSON format

[
  {"path": "src/lib/saveSessionMemory.ts", "description": "2h ago  +12/-3"},
  {"path": "src/hooks/useSessionMemory.ts", "description": "1d ago  +5/-0"}
]

Either option would enable richer file suggestion UX without breaking existing scripts.

Use Cases

• Last modified time: helps users pick the file they were recently working on
• Git diff stats (+12/-3): shows which files have uncommitted changes at a glance
• Branch/status indicators: [modified], [untracked], [staged]
• File size or type hints: useful in large monorepos

Environment

• Claude Code (CLI)
• macOS / Linux
• Using custom fileSuggestion command in .claude/settings.json