INBOX-0: Gmail request inbox backend (MailKit) + Request entity + sync/triage endpoints

- Request entity (GmailMessageId unique, ThreadId, threading headers, From*, Subject, BodyText,
  ReceivedAt, Status enum-as-string New|InProgress|Assigned|Answered|Abandoned, AssignedContactId? FK,
  DraftReply?, AnsweredAt?). MailSettings singleton (GmailAddress, AppPassword ENCRYPTED via Data
  Protection, PollInterval, Folder, LastUid). Migration AddRequestsAndMailSettings.
- IGmailMailReader (mockable) + MailKit GmailMailReader (imap.gmail.com:993 SSL, envelope+X-GM-THRID
  +body). RequestSyncService: dedup on Message-Id, track LastUid. MailKit 4.17.0.
- Endpoints: POST /api/requests/sync, GET /api/requests (Gridify, filter status), GET /api/requests/{id},
  PUT triage (status+assignedContactId), GET/PUT /api/mail-settings (App Password never returned).
- Tests (in-memory DB + canned reader): sync dedup/idempotency/config-guard, HTTP sync->triage->assign,
  mail-settings secrecy. + gitignore the runtime photo-storage/ dir (god housekeeping).

GerbilManagerWebAPI/GerbilManagerWebAPI.csproj

@@ -9,6 +9,7 @@
   <ItemGroup>
     <PackageReference Include="Aspire.Npgsql.EntityFrameworkCore.PostgreSQL" Version="13.4.2" />
     <PackageReference Include="DocumentFormat.OpenXml" Version="3.5.1" />
+    <PackageReference Include="MailKit" Version="4.17.0" />
     <PackageReference Include="Microsoft.AspNetCore.OpenApi" Version="10.0.8" />
     <PackageReference Include="Microsoft.EntityFrameworkCore" Version="10.0.8" />
     <PackageReference Include="Microsoft.EntityFrameworkCore.Design" Version="10.0.8">