Move About-tab copy to HellionStrings and rephrase neutrally

The About tab copy was hand-written in English directly in About.cs,
which left the German users on the upstream Chat 2 wording for the
Hellion-specific blocks. The copy itself also leaned on em-dashes
mid-sentence and on a tone that could read as accusing Chat 2 of
GDPR violations, which was never the intent. This commit moves the
six About-tab sections (Maintainer, Why this fork exists, Built on
Chat 2, License, FFXIV disclaimer, Localization) into HellionStrings
and tightens the wording in both languages.

Tone change is the substantive part. Chat 2's full-history default
is now described as "the right one for most users" rather than a
problem the fork is fixing, and the webinterface removal is framed
as a focus mismatch — Chat 2's webinterface targets remote chat
access from a second device, this fork targets a smaller default
footprint, neither approach is wrong. The personal trigger for the
fork (two million logged messages over two years, mostly /say and
/yell from strangers) stays as it is honest context rather than
criticism.

The same neutralised wording is mirrored in three more places that
described the webinterface removal: the README "Was gegenüber
Chat 2 fehlt" block, the HellionChat.yaml description and changelog,
and the matching repo.json fields. The 0.2.0 changelog no longer
recites the upstream auth-flow internals; "different use case,
substantial rebuild, removed" is enough for users.

Em-dashes were also removed from two body strings that previously
used them as comma replacements (Privacy filter storage-only help
and the retention default description). Heading-level dashes
("Hellion Chat — Welcome", "Export (GDPR Art. 15 — right of
access)") stay because dashes are appropriate as separators in
titles.

The Theme description was already inaccurate — it still talked
about slate-violet tabs and amber highlights even though the brand
sweep moved everything onto Arctic Cyan plus Ember Orange. Updated
to describe the current palette honestly.

ChatTwo/HellionChat.yaml

@@ -3,12 +3,12 @@ author: JonKazama-Hellion
 punchline: Chat 2 with privacy controls aligned to EU, US and JP rules
 description: |-
   Hellion Chat is built on top of Chat 2 with one removal and a stack
-  of privacy controls on top. The /chat2 command, tabs, channel
-  filters, RGB colours, emotes, screenshot mode, IPC integration and
-  the chat replacement window itself work the same. The optional
-  webinterface that Chat 2 ships is intentionally not part of this
-  fork because it could not be hardened to the privacy guarantees
-  Hellion Chat makes by default.
+  of privacy controls on top. Tabs, channel filters, RGB colours,
+  emotes, screenshot mode, IPC integration and the chat replacement
+  window itself work the same. The optional webinterface that Chat 2
+  ships is intentionally not part of this fork because it serves a
+  different use case from the smaller default footprint Hellion Chat
+  is built around.
 
   On top of that, Hellion Chat adds privacy and data-handling controls
   designed to align with the modern data protection rules that apply
@@ -42,15 +42,12 @@ tags:
 changelog: |-
   **Hellion Chat 0.2.0 — Webinterface removed**
 
-  Following an internal security and consistency audit the upstream
-  webinterface has been removed in its entirety. Hardening it to the
-  privacy guarantees Hellion Chat makes by default would have meant
-  rewriting the auth flow (the upstream code uses a five-digit
-  numeric code from System.Random), changing the default bind address
-  (currently every interface), reworking cookie handling and adding
-  the privacy filter to the live message stream that the webinterface
-  was broadcasting around it. The cumulative cost did not match the
-  niche use case for a fork that wants less network surface, not more.
+  The upstream webinterface has been removed in its entirety. It
+  serves a different use case from the smaller default footprint
+  this fork is built around, namely remote access to chat from a
+  second device. Aligning it with the data minimisation defaults
+  Hellion Chat ships with would have meant a substantial rebuild.
+  Removing it was the cleaner path for this particular fork.
 
   What changed in this release: