Migrate Actions workflows to Gitea

- codeql.yml removed: GitHub-only (uses github/codeql-action/*).
- build.yml + release.yml: runs-on switched to ubuntu-latest (Gitea Cloud
  has no Windows runner). Dalamud staging is now downloaded via curl/unzip
  into $HOME/.xlcore/dalamud/Hooks/dev/, the path the Dalamud SDK 15 uses
  on Linux. Locate-step uses find instead of Get-ChildItem.
- release.yml: softprops/action-gh-release replaced with the Gitea-native
  https://gitea.com/actions/release-action. Auto-injected GITHUB_TOKEN on
  Gitea Actions has Gitea-API scope and is sufficient.
- forge-announce.yml: environment: Webhook removed (Gitea has no
  environments — DISCORD_FORGE_WEBHOOK is a repo-level Actions secret).
  avatar_url and embed url switched from raw.githubusercontent.com /
  github.com to gitea.com.
- release-footer.md: install URL plus the five doc links (README, PRIVACY,
  THIRD_PARTY_NOTICES, SECURITY, SUPPORT) and LICENSE link switched to
  gitea.com/.../src/branch/main/. ChatTwo upstream link stays on GitHub.

.github/workflows/build.yml

@@ -3,6 +3,12 @@ name: Build
 # Verifies that every push to main and every PR still builds against the
 # current Dalamud staging branch. Does not produce release artefacts; the
 # release workflow handles that on tag.
+#
+# Linux runner: gitea.com Cloud Actions provides ubuntu-latest. The plugin
+# csproj targets net10.0-windows, but `dotnet build` cross-compiles on
+# Linux as long as the Dalamud staging assemblies are present at the
+# expected lookup path ($(HOME)/.xlcore/dalamud/Hooks/dev/, which the
+# Dalamud SDK 15 uses on Linux).
 
 on:
   push:
@@ -21,7 +27,7 @@ permissions:
 jobs:
   build:
     name: Build (Release)
-    runs-on: windows-latest
+    runs-on: ubuntu-latest
     timeout-minutes: 15
 
     steps:
@@ -34,12 +40,11 @@ jobs:
           dotnet-version: 10.0.x
 
       - name: Download Dalamud staging
-        shell: pwsh
         run: |
-          $hooks = Join-Path $env:APPDATA "XIVLauncher\addon\Hooks\dev"
-          New-Item -ItemType Directory -Force -Path $hooks | Out-Null
-          Invoke-WebRequest -Uri https://goatcorp.github.io/dalamud-distrib/stg/latest.zip -OutFile dalamud.zip
-          Expand-Archive -Force -Path dalamud.zip -DestinationPath $hooks
+          hooks="$HOME/.xlcore/dalamud/Hooks/dev"
+          mkdir -p "$hooks"
+          curl -fsSL https://goatcorp.github.io/dalamud-distrib/stg/latest.zip -o dalamud.zip
+          unzip -oq dalamud.zip -d "$hooks"
 
       - name: Restore
         run: dotnet restore HellionChat/HellionChat.csproj