docs: add What's New With 8.2.0 and fix three doc gaps

[lmajano]

Summary

• Adds a new consolidated release-notes page, readme/release-history/whats-new-with-8.2.0.md, covering everything shipped since v8.1.0: route-scoped middleware, HTTP caching primitives (ETag/Last-Modified/Cache-Control), first-class Server-Sent Events, AI routing conversational context, a security hardening fix to HTTP method spoofing, and Renderer/routing performance work. Links to SUMMARY.md.
• Fixes three documentation gaps found while grounding that page against the merged code in ColdBox/coldbox-platform since v8.1.0:
  • the-basics/routing/http-method-spoofing.md described the old, unrestricted _method override behavior (a GET request could spoof DELETE). Rewritten to document the new POST-only restriction, the security rationale, a behavior table, and the new event.getOriginalHTTPMethod().
  • the-basics/layouts-and-views/views/view-caching.md had no mention of the new viewDiscoveryCaching setting. Added a "View Discovery Caching" section distinguishing it from viewCaching.
  • the-basics/interceptors/custom-events/announcing-interceptions.md didn't document that announce() now returns true/false to report whether an interceptor short-circuited the chain. Added a "Detecting a Short-Circuit" section.

This PR is independent of any other pending documentation PR in this repo — it touches different files than #292/#293/#294, all of which are already merged into v8.x.

Test plan

• Confirmed readme/release-history/whats-new-with-8.2.0.md exists and is listed in SUMMARY.md.
• Verified all 9 internal links in the new page resolve to existing files in the repo (middleware.md, middleware-groups.md, http-caching.md, server-sent-events.md, sse-routes.md, ai-routing.md, http-method-spoofing.md, view-caching.md#view-discovery-caching, announcing-interceptions.md#detecting-a-short-circuit).
• Confirmed the two new anchor targets (#view-discovery-caching, #detecting-a-short-circuit) match their new headings.
• Confirmed the http-method-spoofing.md rewrite preserves the original intro, form example, and startForm() example verbatim, with new content appended after.

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