perf(search): keyset pagination + fix the format-gate line-ending flip-flop

RECOMMENDATIONS #8: additive AfterSentAtUtc+AfterId cursor — browse windows fetch
via a (SentAtUtc, Id) keyset filter, O(pageSize) at any depth, COUNT skipped
(TotalCount=-1). Adds the Id tie-break to browse ordering (fixes latent
duplicate/skip on equal timestamps). Verified: InMemory continuation test + a
live-Postgres throwaway proving the Guid cursor comparison translates (removed).

Also root-causes the recurring pre-commit/CI format failures: dotnet-format on
Windows defaulted to CRLF while .gitattributes stores LF — the two fought forever.
Adds .editorconfig (end_of_line=lf etc.) so every tool agrees, and normalises the
straggler files. This bug bit three separate commits before being diagnosed.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

src/InboxIntel.Infrastructure/Migrations/20260630140733_InitialCreate.cs

@@ -1,4 +1,4 @@
-using System;
+using System;
 using Microsoft.EntityFrameworkCore.Migrations;
 using NpgsqlTypes;
 

src/InboxIntel.Infrastructure/Migrations/20260630200946_AddUserDigestFields.cs

@@ -1,4 +1,4 @@
-using System;
+using System;
 using Microsoft.EntityFrameworkCore.Migrations;
 
 #nullable disable

src/InboxIntel.Infrastructure/Migrations/20260630201607_AddUnsubscribeConfidence.cs

@@ -1,4 +1,4 @@
-using Microsoft.EntityFrameworkCore.Migrations;
+using Microsoft.EntityFrameworkCore.Migrations;
 
 #nullable disable
 

src/InboxIntel.Infrastructure/Migrations/20260701192100_WeightSearchVectorSubjectBody.cs

@@ -1,4 +1,4 @@
-using Microsoft.EntityFrameworkCore.Migrations;
+using Microsoft.EntityFrameworkCore.Migrations;
 using NpgsqlTypes;
 
 #nullable disable

src/InboxIntel.Infrastructure/Migrations/20260701203001_EnablePgTrgm.cs

@@ -1,4 +1,4 @@
-using Microsoft.EntityFrameworkCore.Migrations;
+using Microsoft.EntityFrameworkCore.Migrations;
 
 #nullable disable
 

src/InboxIntel.Infrastructure/Migrations/20260701235112_TrigramIndexesSenderDomain.cs

@@ -1,4 +1,4 @@
-using Microsoft.EntityFrameworkCore.Migrations;
+using Microsoft.EntityFrameworkCore.Migrations;
 
 #nullable disable
 

src/InboxIntel.Infrastructure/Migrations/20260702002304_AddEmbeddingColumn.cs

@@ -1,4 +1,4 @@
-using Microsoft.EntityFrameworkCore.Migrations;
+using Microsoft.EntityFrameworkCore.Migrations;
 using Pgvector;
 
 #nullable disable