refactor: SonarQube code-smell & duplication cleanup

[HandyS11]

Cleans up the SonarQube maintainability smells (82) and the structural duplication (8.4% density, 1,551 lines), sequenced low-risk → high-risk with the test suite green at every commit.

What changed

Mechanical:

• chore(sonar): exclude auto-generated EF migrations + obj/bin from analysis (CPD noise).
• style: analyzer auto-fixes (collection init, var, switch expr, UTF-8 literals). Two fixes deliberately left as-is where they conflict with other analyzers (nested-ternary S3358, primary-ctor CA2000).
• S1192: extracted repeated string literals to private const.
• IDE0130: moved 8 RustPlusBot.Abstractions.Connections types to the namespace matching their folder, updating ~69 consumers (the shared using was kept where genuine Features.Connections.Listening types are still referenced).

Structural (the duplication):

• RustPlusBot.Localization (new project): shared ILocalizer + DictionaryLocalizer replace 6 byte-identical per-feature localizer implementations. The 6 IXLocalizer interfaces are kept as thin markers extending the shared one, so per-feature DI registrations stay distinct (no last-wins collision). Resolves the in-code "consolidate into a shared project" TODO.
• CachingChannelLocator: abstract base + 5 sealed subclasses collapse the near-identical Event/Map/Switch/Alarm/TeamChat locators (each was ~75 lines → ~10).
• DiscordChannelMessenger: shared post/edit boilerplate for 4 posters (Switch/Alarm self-heal EnsureAsync, Event/Player fire-and-forget PostAsync). The Map poster (posts a file) and Alarm's SendEveryonePingAsync are intentionally left separate.

Other smells:

• S107: bundled cohesive constructor dependencies into record types on 6 ctors + 1 method (all now ≤7 params).
• S3776: extracted helpers to drop cognitive complexity <15 in MapRenderer.DrawPlayers, ServerInfoMessageRenderer.RenderAsync, ConnectionSupervisor.RunConnectedAsync.

Notes for review

• Net −205 LOC despite adding a new project + its tests.
• 531 tests across 13 assemblies green; dotnet jb cleanupcode --profile=ReformatAndReorder produces zero diff (format gate passes).
• TeamChat's ResolveAsync moved from an O(1) dedicated reverse-dict to an O(n) scan of the forward map — equivalent under the data model (a channel can't map to two server keys), negligible volume.
• The poster extraction incidentally fixed a pre-existing structured-log bug where {MessageId}/{ChannelId} were bound to swapped values (human-readable message unchanged).
• The empirical SonarQube smell/duplication delta will only show after this lands on develop — Community-Edition Sonar analyzes the single long-lived branch only.

🤖 Generated with Claude Code