docs: hold the documentation against the code

Every claim in the user-facing docs, checked against what the plugin
actually does after A2 to A5.

The two GDPR sections in PRIVACY.md describe features that only exist
again as of this cycle, so they now name the screens they live on and
say what the cleanup does with a channel this build does not recognise.
The export sentence promised a date range; the form offers an age in
days.

PRIVACY.md also named "Show emotes" in Settings as the way to stop the
one outbound call the plugin makes. That switch has had no control since
May, and a documented opt-out that only exists in the JSON is not an
opt-out, so the toggle is back in the chat tab. Both its strings were
already translated.

Dead paths: the README source tree still listed a file deleted in May,
docs/IPC.md cited a window that no longer exists, the first-run wizard
pointed at the same removed file, and the theme authoring guide sent
readers to a Themes tab that is called Appearance.

The changelog lost two double blank lines that were failing markdownlint
and holding preflight red. Preflight is green again.

Historical documents keep their old paths on purpose: the changelog and
the AI disclosure describe what was true when they were written.

docs/CHANGELOG.md

@@ -130,7 +130,6 @@ release stays at v1.5.6.
 - Test suite 829 → 892, and `StatusBarCacheTests` is back in the build after sitting in the
   exclusion block.
 
-
 ## [1.9.0] — unreleased (local only)
 
 Polish, tester-beta preparation and a concurrency hardening pass. **Not published** — the public
@@ -164,7 +163,6 @@ the assembly version reads 1.9.0.
 - Removed `DeferredSaveFrames`: the debounce was fully wired but never armed.
 - Test suite 812 → 829, including migration and query-plan coverage.
 
-
 ## Hellion Chat 1.5.6 — Settings Overhaul + Filter & Notification Polish (2026-05-23)
 
 - Settings window reorganised: ten tabs down to seven (General, Appearance, Chat, Window, Channels, Data & Privacy, About). Each tab now uses collapsible sections grouped by control type. Sections start collapsed every time you open a tab — less noise, easier to find what you need.