chore(release): v1.5.1 manifest bump

- csproj <Version> 1.5.0 to 1.5.1; <None Include="images\**"> now
  excludes the source-only ASCII study folder so the deploy stays
  clean
- yaml + repo.json changelog block prepended with the v1.5.1 entry,
  v1.4.8 trimmed out per the slim rule (three to four versions in
  the manifest cache, older history lives on the Gitea release page)
- repo.json AssemblyVersion + TestingAssemblyVersion bumped to
  1.5.1.0, three DownloadLink* URLs point at v1.5.1
- docs/CHANGELOG and docs/ROADMAP gain the v1.5.1 entry; ROADMAP
  Next-Cycle slot moves to v1.5.2 First-Run-Wizard rework
- README status sections updated, the previous v1.5.0 paragraph
  kept under a "Project status (pre-v1.5.1, kept for context)"
  heading
- Forge-post .github/forge-posts/v1.5.1.md added, DE body honest
  about the HITCH-win miss
- yamllint config ignores the plugin manifest yaml because it
  follows DalamudPackager's 4-space indent convention rather than
  yamllint's default 2

Changelogs are honest about the cross-plugin HITCH target from
v1.5.0 not landing this cycle.

.yamllint.yaml

@@ -12,6 +12,12 @@
 
 extends: default
 
+# Plugin-Manifest folgt DalamudPackager-Konvention (4-space-indent für
+# image_urls + tags). yamllint-Default verlangt 2 — Konflikt, daher
+# ignorieren statt das Manifest zu reformatieren.
+ignore: |
+  HellionChat/HellionChat.yaml
+
 rules:
   # Zeilenlängen-Check aus (konsistent mit markdownlint MD013)
   line-length: disable