feat(influxdb3): add runtime architecture, metrics monitoring, and performance tuning documentation

- Add comprehensive runtime architecture documentation covering thread pools, resource allocation, and concurrency model
- Add metrics monitoring guide with Prometheus endpoint configuration and key metrics reference
- Add performance tuning documentation with thread pool optimization, memory settings, and resource planning
- Add clustering configuration documentation for InfluxDB 3 Enterprise
- Update CLI serve command documentation with new runtime and metrics flags

This addresses the need for detailed documentation on:
- How InfluxDB 3 manages threads and system resources
- How to monitor and observe InfluxDB 3 performance metrics
- How to tune runtime parameters for optimal performance
- How to configure clustering in Enterprise deployments

Closes #6403

Author: jstirnaman

.github/instructions/content.instructions.md

@@ -219,4 +219,4 @@ For the complete shortcodes reference, see `/.github/instructions/shortcodes-ref
 - Format code examples to fit within 80 characters
 - Use long options in command line examples (`--option` instead of `-o`)
 - Use GitHub callout syntax for notes and warnings
-- Image naming: `project/version-context-description.png`
+- Image naming: `project/version-context-description.png`

content/influxdb3/core/admin/monitor-metrics.md

@@ -0,0 +1,22 @@
+---
+title: Monitor metrics
+seotitle: Monitor InfluxDB 3 Core metrics
+description: >
+  Access and understand Prometheus-format metrics exposed by {{< product-name >}}
+  to monitor system performance, resource usage, and operational health.
+menu:
+  influxdb3_core:
+    parent: Administer InfluxDB
+    name: Monitor metrics
+weight: 105
+influxdb3/core/tags: [monitoring, metrics, prometheus, observability, operations]
+related:
+  - /influxdb3/core/reference/internals/runtime-architecture/
+  - /influxdb3/core/admin/performance-tuning/
+  - /influxdb3/core/reference/telemetry/
+source: /shared/influxdb3-admin/monitor-metrics.md
+---
+
+<!--
+//SOURCE - content/shared/influxdb3-admin/monitor-metrics.md
+-->

content/influxdb3/core/admin/performance-tuning.md

@@ -0,0 +1,22 @@
+---
+title: Performance tuning
+seotitle: InfluxDB 3 Core performance tuning and optimization
+description: >
+  Optimize InfluxDB 3 Core performance by tuning thread allocation,
+  memory settings, and other configuration options for your specific workload.
+weight: 205
+menu:
+  influxdb3_core:
+    parent: Administer InfluxDB
+    name: Performance tuning
+related:
+  - /influxdb3/core/reference/internals/runtime-architecture/
+  - /influxdb3/core/reference/config-options/
+  - /influxdb3/core/admin/query-system-data/
+source: /shared/influxdb3-admin/performance-tuning.md
+---
+
+<!--
+The content of this file is located at
+//SOURCE - content/shared/influxdb3-admin/performance-tuning.md
+-->

content/influxdb3/core/object-storage/_index.md

@@ -7,7 +7,7 @@ menu:
   influxdb3_core:
     name: Configure object storage
     parent: Administer InfluxDB
-weight: 110
+weight: 100
 influxdb3/core/tags: [object storage, S3]
 related:
   - /influxdb3/core/reference/config-options/

content/influxdb3/core/reference/cli/influxdb3/serve.md

@@ -83,6 +83,7 @@ influxdb3 serve [OPTIONS] --node-id <HOST_IDENTIFIER_PREFIX>
 |                  | `--log-filter`                                       | _See [configuration options](/influxdb3/core/reference/config-options/#log-filter)_                                       |
 |                  | `--log-format`                                       | _See [configuration options](/influxdb3/core/reference/config-options/#log-format)_                                       |
 |                  | `--max-http-request-size`                            | _See [configuration options](/influxdb3/core/reference/config-options/#max-http-request-size)_                            |
+|                  | `--num-io-threads`                                   | _See [configuration options](/influxdb3/core/reference/config-options/#num-io-threads)_                                   |
 |                  | `--object-store-cache-endpoint`                      | _See [configuration options](/influxdb3/core/reference/config-options/#object-store-cache-endpoint)_                      |
 |                  | `--object-store-connection-limit`                    | _See [configuration options](/influxdb3/core/reference/config-options/#object-store-connection-limit)_                    |
 |                  | `--object-store-http2-max-frame-size`                | _See [configuration options](/influxdb3/core/reference/config-options/#object-store-http2-max-frame-size)_                |

content/influxdb3/core/reference/internals/runtime-architecture.md

@@ -0,0 +1,23 @@
+---
+title: Runtime thread architecture
+seotitle: InfluxDB 3 Core runtime thread architecture
+description: >
+  Learn how InfluxDB 3 Core allocates and manages runtime threads between IO and DataFusion thread pools
+  for optimal performance.
+weight: 102
+menu:
+  influxdb3_core:
+    parent: Core internals
+    name: Runtime architecture
+influxdb3/core/tags: [architecture, threads, runtime, performance]
+related:
+  - /influxdb3/core/admin/performance-tuning/
+  - /influxdb3/core/reference/config-options/
+  - /influxdb3/core/admin/monitor-metrics/
+source: /shared/influxdb3-internals-reference/runtime-architecture.md
+---
+
+<!--
+The content of this file is located at
+//SOURCE - content/shared/influxdb3-internals-reference/runtime-architecture.md
+-->

content/influxdb3/core/reference/metrics.md

@@ -0,0 +1,18 @@
+---
+title: Metrics
+seotitle: InfluxDB 3 Core metrics reference
+description: >
+  InfluxDB 3 Core exposes Prometheus-format metrics,
+  including descriptions, types, and labels for monitoring and observability.
+menu:
+  influxdb3_core:
+    parent: Reference
+weight: 106
+influxdb3/core/tags: [metrics, prometheus, monitoring, reference, observability]
+source: /shared/influxdb3-reference/metrics.md
+---
+
+<!--
+The content of this file is located at
+//SOURCE - content/shared/influxdb3-reference/metrics.md
+-->