docs: add missing alt attributes to documentation images

Add context-aware alt text to 36 images across 20 MDX files flagged
by mint a11y. Descriptions are derived from each image's caption and
surrounding step text. Part of fosrl/docs-v2#116.

manage/analytics/access.mdx

@@ -26,7 +26,7 @@ Authentication logs capture authentication events when users or API keys attempt
 - Analyzing user agent and device information
 
 <Frame>
-  <img src="/images/access_logs.png" centered/>
+  <img src="/images/access_logs.png" alt="Authentication logs table in the Pangolin dashboard" centered/>
 </Frame>
 
 <Tip>Make sure to enable authentication logs in the org settings</Tip>

manage/analytics/action.mdx

@@ -26,7 +26,7 @@ Admin Action logs capture administrative events and configuration changes perfor
 - Meeting security and compliance requirements
 
 <Frame>
-  <img src="/images/action_logs.png" centered/>
+  <img src="/images/action_logs.png" alt="Admin action logs table in the Pangolin dashboard" centered/>
 </Frame>
 
 <Tip>Make sure to enable access logs in the org settings</Tip>

manage/analytics/request.mdx

@@ -23,7 +23,7 @@ HTTPS Request logs capture every HTTPS request that passes through a reverse pro
 - Troubleshooting connectivity and routing issues
 
 <Frame>
-  <img src="/images/request_logs.png" centered/>
+  <img src="/images/request_logs.png" alt="HTTPS request logs table in the Pangolin dashboard" centered/>
 </Frame>
 
 ## HTTPS Request Log Fields

manage/analytics/streaming.mdx

@@ -22,7 +22,7 @@ Open **Organization → Logs & Analytics → Streaming** to add destinations and
 You choose which categories each destination receives. Only log types enabled for your organization can be streamed.
 
 <Frame>
-  <img src="/images/streaming-log-types.png" centered />
+  <img src="/images/streaming-log-types.png" alt="Log type selection for a streaming destination" centered />
 </Frame>
 
 ## Destination types
@@ -30,7 +30,7 @@ You choose which categories each destination receives. Only log types enabled fo
 Each destination type has its own configuration and payload behavior. Select **Add destination** and pick a delivery method.
 
 <Frame>
-  <img src="/images/streaming-add-destination.png" centered />
+  <img src="/images/streaming-add-destination.png" alt="Add destination dialog in the Pangolin dashboard" centered />
 </Frame>
 
 <CardGroup cols={2}>

manage/analytics/streaming/http.mdx

@@ -36,7 +36,7 @@ On the **Settings** tab, set a display name, the endpoint URL, and authenticatio
 | Custom header | A single header name and value (for example an API key header) |
 
 <Frame>
-  <img src="/images/streaming-http-settings.png" centered />
+  <img src="/images/streaming-http-settings.png" alt="HTTP destination settings with URL and authentication options" centered />
 </Frame>
 
 All delivery uses **POST**. Requests time out after 30 seconds.
@@ -46,7 +46,7 @@ All delivery uses **POST**. Requests time out after 30 seconds.
 On the **Headers** tab, add optional static headers sent with every request, for example a vendor-specific API key or a non-default `Content-Type`. When you do not override it, Pangolin sends `Content-Type: application/json` (or `application/x-ndjson` when using the NDJSON payload format).
 
 <Frame>
-  <img src="/images/streaming-http-headers.png" centered />
+  <img src="/images/streaming-http-headers.png" alt="Headers tab for adding static HTTP headers" centered />
 </Frame>
 
 ## Default payload (template off)
@@ -83,7 +83,7 @@ Some columns are stored as JSON strings in the database (`headers`, `query`, and
 On the **Body** tab, enable **Custom body template** and provide a JSON template string. Pangolin performs simple placeholder substitution, **not** a full templating language like Handlebars.
 
 <Frame>
-  <img src="/images/streaming-http-body.png" centered />
+  <img src="/images/streaming-http-body.png" alt="Body tab with custom body template editor" centered />
 </Frame>
 
 ### Template variables

manage/analytics/streaming/s3.mdx

@@ -38,7 +38,7 @@ Configure:
 Pangolin uses static access keys only. There is no IAM role, instance profile, or OIDC picker in the UI.
 
 <Frame>
-  <img src="/images/streaming-s3-settings.png" centered />
+  <img src="/images/streaming-s3-settings.png" alt="S3 destination settings with credentials, region, and bucket" centered />
 </Frame>
 
 Uploads time out after 60 seconds per object.
@@ -56,7 +56,7 @@ Uploads time out after 60 seconds per object.
 | **CSV** | RFC-4180 CSV with a header row; see [CSV format](#csv-format) |
 
 <Frame>
-  <img src="/images/streaming-s3-format.png" centered />
+  <img src="/images/streaming-s3-format.png" alt="Format tab with file format and gzip options" centered />
 </Frame>
 
 ## Logs tab
@@ -64,7 +64,7 @@ Uploads time out after 60 seconds per object.
 Choose which log categories are uploaded. Each enabled type is written to its own key prefix (`request/`, `action/`, etc.). Only log types enabled for your organization can be streamed.
 
 <Frame>
-  <img src="/images/streaming-s3-logs.png" centered />
+  <img src="/images/streaming-s3-logs.png" alt="Logs tab for selecting streamed log types" centered />
 </Frame>
 
 ## Object key layout