homepage copy refresh + fix skills CLI installation (#539)

* add wiki/betterstack.md documenting log querying, request-ID grouping, and MCP usage

Made-with: Cursor

* fix webhook race conditions: separate runId assignment from data updates

the workflow_run webhook handler had a race where concurrent handlers assigned
the same runId to different pending records. the loser's P2002 silently dropped
data updates (jobId, status, completedAt). fix by splitting into two steps:
assignRunId() handles the race-safe unique assignment, then data updates always
target where: { runId } so they hit the correct record regardless of who won.

also downgrade R2 ObjectLockedByBucketPolicy errors from error to warn level
since duplicate webhook deliveries writing the same key is expected under load.

Made-with: Cursor

* homepage copy refresh + fix skills CLI installation

- update hero to "Agent x GitHub" with new subtagline
- rewrite intro paragraphs: workflow, harness capabilities, billing
- add feature sections: bash isolation, headless browser, MCP tools
- update FAQ answers, footer attribution, free-for-oss copy
- update APP_DESCRIPTION for SEO
- fix skills install: use npx from tmpdir instead of local binary
  (the bundled action has no node_modules; running npx from tmpdir
  avoids project .npmrc with pnpm settings breaking binary resolution)
- instruct agents to use markdown image syntax in upload_file tool
- start dependency installation eagerly from main.ts
- include event title in task instructions

Made-with: Cursor

main.ts

@@ -2,6 +2,7 @@
 
 import * as core from "@actions/core";
 import { deleteProgressComment, reportProgress } from "./mcp/comment.ts";
+import { startInstallation } from "./mcp/dependencies.ts";
 import {
   initToolState,
   startMcpHttpServer,
@@ -307,6 +308,8 @@ export async function main(): Promise<MainResult> {
     log.info(`» MCP server started at ${mcpHttpServer.url}`);
     timer.checkpoint("mcpServer");
 
+    startInstallation(toolContext);
+
     if (payload.model) log.info(`» model:   ${payload.model}`);
     if (payload.timeout) log.info(`» timeout: ${payload.timeout}`);
     log.info(`» push:    ${payload.push}`);