docs(seo): rewrite top-impression page titles, fix AWX/Makefile search noise

[ndreno]

Summary

• Reworded SUMMARY.md entries (and matching H1s) for the high-impression docs pages: control plane, middlewares, dispatchers, getting started, CLI reference, dev setup, plugin development, spec configuration
• Also moved those entries to sentence case
• Rephrased the parenthetical and heading on control-plane.md that contained the exact phrase 'running the UI development', which was attracting AWX/Makefile-related search traffic

Why

Last 90 days of Search Console data:

Page	Impressions	Avg position	Clicks
guide/control-plane.html	151	2.34	0
guide/middlewares.html	79	6.68	0
contributing/development.html	78	9.22	0
guide/dispatchers.html	31	9.77	1
reference/cli.html	23	8.78	0

The pages rank but don't get clicks. mdBook uses the SUMMARY.md entry as the <title> tag - generic titles like 'Control Plane - Barbacane Documentation' don't sell the page in the SERP. New titles lead with the function ('Control plane (REST API)', 'WASM plugin development') so the SERP snippet is more clickable.

The AWX/Makefile noise was a single GSC query ('running the ui development' awx or makefile) at position 1 with 31 impressions and 0 clicks - users searching for AWX docs were getting our page instead. Rephrasing breaks the exact-phrase match.

Test plan

• Run mdbook build locally and verify the rendered <title> tag on the touched pages
• Confirm the sidebar still reads cleanly (longer entries should still wrap fine)
• After merge, request reindex in Search Console for the changed URLs