feat: add telemetry engine for distributed tracing (#326)

* feat: add telemetry engine for distributed tracing

Adds a comprehensive telemetry system for collecting and reporting agent traces
to hosted or self-hosted observability endpoints.

Features:
- Trace collection with spans for generation lifecycle
- Token usage tracking (input, output, thinking)
- Tool call tracing with timing
- Error recording with backtraces
- Async HTTP reporting with batching
- Configurable sampling rate
- Auto-instrumentation via railtie

Configuration via YAML:
  telemetry:
    enabled: true
    endpoint: https://api.activeagents.ai/v1/traces
    api_key: your-api-key
    sample_rate: 1.0

Or programmatically:
  ActiveAgent::Telemetry.configure do |config|
    config.enabled = true
    config.endpoint = "https://..."
    config.api_key = "..."
  end

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude <noreply@anthropic.com>

* feat: add dashboard engine for telemetry visualization

This adds a Rails Engine to the ActiveAgent gem that provides:
- TelemetryTrace model for storing traces
- TracesController for viewing traces in a dashboard
- API::TracesController for ingesting traces
- ProcessTelemetryTracesJob for async trace processing
- ERB views with Tailwind CSS for the dashboard UI
- Install generator for migrations and configuration

The dashboard supports two modes:
- Local mode: Single-tenant, no auth, synchronous processing
- Multi-tenant mode: Account association, API key auth, async processing

Configuration options:
- multi_tenant: Enable multi-tenant mode
- account_class: Class name for Account model
- current_account_method: Controller method to get current account
- trace_model_class: Custom trace model class
- use_inertia: Enable React/Inertia frontend
- authentication_method: Custom auth callback

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude <noreply@anthropic.com>

* fix: rename create_migration to avoid Rails conflict

The method name 'create_migration' conflicts with
ActiveRecord::Generators::Migration module internals.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude <noreply@anthropic.com>

* feat(dashboard): Add engine models, jobs, and install generator

- Add Agent, AgentRun, AgentVersion, AgentTemplate models
- Add SandboxSession, SandboxRun models
- Add SessionRecording, RecordingAction, RecordingSnapshot models
- Add AgentExecutionJob, SandboxProvisionJob, SandboxCleanupJob
- Add install generator with migrations
- Add DashboardController for root view
- Fix RuboCop: exclude generator templates from linting
- Fix style issues (array bracket spacing)

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude <noreply@anthropic.com>

---------

Co-authored-by: Claude <noreply@anthropic.com>

Author: TonsOfFun

.rubocop.yml

@@ -15,6 +15,7 @@ AllCops:
     - "test/dummy/tmp/**/*"
     - "node_modules/**/*"
     - "vendor/**/*"
+    - "lib/generators/**/templates/**/*"
 
 Style/StringLiterals:
   EnforcedStyle: double_quotes

.tool-versions

@@ -1 +1,2 @@
 nodejs 24.7.0
+ruby 3.4.8

docs/.vitepress/config.mts

@@ -99,6 +99,7 @@ export default defineConfig({
           { text: 'Providers', link: '/providers' },
           { text: 'Configuration', link: '/framework/configuration' },
           { text: 'Instrumentation', link: '/framework/instrumentation' },
+          { text: 'Telemetry', link: '/framework/telemetry' },
           { text: 'Retries', link: '/framework/retries' },
           { text: 'Rails Integration', link: '/framework/rails' },
           { text: 'Testing', link: '/framework/testing' },

docs/.vitepress/theme/style.css

@@ -102,7 +102,7 @@
     rgb(255, 100, 100) 20%,
     rgb(250, 52, 59) 40%,
     rgb(255, 100, 100) 60%,
-    rgb(250, 52, 59) 100%
+    rgb(250, 52, 59) 80%
   );
 
   --vp-home-hero-image-background-image: radial-gradient(