feat(reasoning): full /reasoning CLI parity — show|hide + effort levels via config.yaml (#812)

Closes #461

Adds full /reasoning CLI parity to the WebUI slash command system:

- /reasoning show|on → window._showThinking = true; writes display.show_reasoning to config.yaml (same key as CLI); mirrors to settings.json for boot.js
- /reasoning hide|off → same in reverse; re-renders immediately
- /reasoning none|minimal|low|medium|high|xhigh → POST /api/reasoning → writes agent.reasoning_effort to config.yaml; takes effect next turn (matching CLI semantics)
- /reasoning (no args) → GET /api/reasoning → live status toast from config.yaml
- Autocomplete shows all 8 options: show|hide|none|minimal|low|medium|high|xhigh
- Profile-isolated: _get_config_path() is thread-local so per-profile settings never bleed across
- Boot hydration: window._showThinking initialised from settings.json show_thinking on page load
- Inspect.signature guard in streaming.py so older hermes-agent builds don't TypeError

28 new tests, 1708/1708 total passing. Full browser QA on port 8789 with isolated state. CLI/config.yaml sync verified with hermes_constants.parse_reasoning_effort().

static/boot.js

@@ -764,6 +764,7 @@ function applyBotName(){
     window._showCliSessions=!!s.show_cli_sessions;
     window._soundEnabled=!!s.sound_enabled;
     window._notificationsEnabled=!!s.notifications_enabled;
+    window._showThinking=s.show_thinking!==false;
     window._sidebarDensity=(s.sidebar_density==='detailed'?'detailed':'compact');
     window._botName=s.bot_name||'Hermes';
     const appearance=_normalizeAppearance(s.theme,s.skin);
@@ -785,6 +786,7 @@ function applyBotName(){
     window._showCliSessions=false;
     window._soundEnabled=false;
     window._notificationsEnabled=false;
+    window._showThinking=true;
     window._sidebarDensity='compact';
     window._botName='Hermes';
     _bootSettings={check_for_updates:false};