Encrypt Discord token at rest in settings file (machine-bound) (#1491)

* Initial plan

* Add token encryption when saving/loading settings

Co-authored-by: Tyrrrz <1935960+Tyrrrz@users.noreply.github.com>

* Apply suggestion from @Tyrrrz

* Apply suggestion from @Tyrrrz

* Bind token encryption key to machine identity

Co-authored-by: Tyrrrz <1935960+Tyrrrz@users.noreply.github.com>

* Switch to AES-GCM, hex encoding, and GetBytes/Fill improvements

Co-authored-by: Tyrrrz <1935960+Tyrrrz@users.noreply.github.com>

* Address all review feedback: salt injection, code style, localization formatting

Co-authored-by: Tyrrrz <1935960+Tyrrrz@users.noreply.github.com>

* Address latest review: ThisAssembly.Project, EnvironmentExtensions, inline Lazy, renames, localization wording

Co-authored-by: Tyrrrz <1935960+Tyrrrz@users.noreply.github.com>

* Address latest review: layout comment, cipherSource, else block, MachineName fallback, csproj ordering

Co-authored-by: Tyrrrz <1935960+Tyrrrz@users.noreply.github.com>

* Apply suggestion from @Tyrrrz

* Rename GetMachineId→TryGetMachineId, refactor Write to use single array with FillBytes

Co-authored-by: Tyrrrz <1935960+Tyrrrz@users.noreply.github.com>

* Rename cipherSource→cipher in Read(), tokenBytes→tokenData in Write(), update layout comments

Co-authored-by: Tyrrrz <1935960+Tyrrrz@users.noreply.github.com>

* Add cipherSource variable in Write(), update layout comment with size annotation

Co-authored-by: Tyrrrz <1935960+Tyrrrz@users.noreply.github.com>

* Fix CSharpier formatting: inline multiline string assignments and reformat exception filter

Co-authored-by: Tyrrrz <1935960+Tyrrrz@users.noreply.github.com>

* Quote EncryptionSalt argument to handle single quotes in secret value

Co-authored-by: Tyrrrz <1935960+Tyrrrz@users.noreply.github.com>

* Revert double-quote fix on EncryptionSalt argument

Co-authored-by: Tyrrrz <1935960+Tyrrrz@users.noreply.github.com>

* Apply suggestion from @Tyrrrz

* Apply suggestion from @Copilot

Co-authored-by: Copilot <175728472+Copilot@users.noreply.github.com>

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Co-authored-by: copilot-swe-agent[bot] <198982749+Copilot@users.noreply.github.com>
Co-authored-by: Tyrrrz <1935960+Tyrrrz@users.noreply.github.com>
Co-authored-by: Copilot <175728472+Copilot@users.noreply.github.com>

.github/workflows/main.yml

@@ -127,6 +127,7 @@ jobs:
           dotnet publish ${{ matrix.app }}
           -p:Version=${{ github.ref_type == 'tag' && github.ref_name || format('999.9.9-ci-{0}', github.sha) }}
           -p:CSharpier_Bypass=true
+          -p:EncryptionSalt=${{ secrets.ENCRYPTION_SALT || 'HimalayanPinkSalt' }}
           -p:PublishMacOSBundle=${{ startsWith(matrix.rid, 'osx-') }}
           --output ${{ matrix.app }}/bin/publish/
           --configuration Release