fix: remove 3 phantom lifecycle hooks from strray-hermes plugin

[htafolla]

Problem

Plugin startup prints 3 warnings every session:

Plugin 'strray-hermes' registered unknown hook 'on_file_write' (valid: on_session_end, on_session_start, post_llm_call, post_tool_call, pre_llm_call, pre_tool_call)
Plugin 'strray-hermes' registered unknown hook 'on_validation_result'
Plugin 'strray-hermes' registered unknown hook 'on_error'

The host only supports 6 hooks. The plugin declared 5 (2 real + 3 phantom).

Root cause

The three hooks (on_file_write, on_validation_result, on_error) were aspirational — the framework never added them as dispatchable hook types. The Python code wrapped their registration in try/except so it didn't crash, but:

1. plugin.yaml still declared them in provides_hooks, triggering validation warnings at discovery time (before the try/except runs)
2. The handlers were dead code — _modified_files and _validation_results were write-only (never consumed by anything)
3. _on_error's bridge_errors increment was redundant with _call_bridge's own error counting

Fix

• Remove 3 phantom hooks from plugin.yaml provides_hooks
• Remove 3 handler functions + 3 tracking lists + registration loop from __init__.py
• Remove TestLifecycleHooks test class (9 tests for dead code)
• Update hook count in log messages and docs (5 → 2 hooks)
• 120/120 tests pass