Feature: Silent hook option to suppress progress display on successful execution

[multicam]

Summary

Hooks that succeed silently (exit code 0, no stdout) still produce a 3-line progress block in the TUI for PreToolUse, PostToolUse, Stop, and SubagentStop events. For users running multiple hooks per tool call, this produces 12-18 lines of progress blocks per invocation -- 360-900 lines of noise in a typical session.

Current behavior

Every hook execution on PreToolUse/PostToolUse/Stop/SubagentStop renders:

     Hooks PostToolUse → Grep
         └─ Execute ~/.local/bin/agent-hooks audit-log
         └─ Result : Exit code: 0

The suppressOutput JSON field only hides stdout content from transcript mode -- it does not suppress the hook runner's progress display.

Proposed behavior

Add a "silent": true option to hook registrations:

 {
   "hooks": {
     "PostToolUse": [
       {
         "matcher": "*",
         "hooks": [
           {
             "type": "command",
             "command": "~/.local/bin/agent-hooks audit-log",
             "timeout": 3,
             "silent": true
           }
         ]
       }
     ]
   }
 }

When silent: true:
• Hook exits 0 with no stdout/stderr: show nothing in the TUI
• Hook exits non-zero or produces stderr: show the progress block as normal
• Debug mode (--debug): always show full progress regardless of silent

Alternative: global toggle

 {
   "hookProgressDisplay": "errors-only" | "always"
 }

Default always. errors-only hides progress for hooks that exit 0 with no output.

Use case

Most hooks are infrastructure -- audit logging, state tracking, background formatting. They succeed silently 99% of the time.
A silent option keeps the safety net (hooks still run, failures still surface) while eliminating TUI noise.

Prior art

• anthropics/claude-code#9340 (anthropics/claude-code#9340) -- --quiet flag for tool output suppression. Open, 20+ +1s.
• anthropics/claude-code#39499 (anthropics/claude-code#39499) -- "silent": true on hook JSON for Stop hooks. Closed (not_planned), stale.
• anthropics/claude-code#16051 (anthropics/claude-code#16051) -- Hooks show "error" label even on success. Closed (not_planned).