Add nested posts UI (#5)

## Summary
- Cut hunt, question, submission, voting, hiding, and profile flows over to unified posts
- Render nested replies with permission-aware inline Reply/Edit controls and edited markers
- Add post profile queries and the author index migration they depend on

Co-authored-by: codegirl-007 <s.raide@gmail.com>

internal/store/migrate_posts_test.go

@@ -138,6 +138,18 @@ WHERE schemaname = current_schema()
 	if postVoteIndexCount != 1 {
 		t.Fatalf("post vote index count = %d, want 1", postVoteIndexCount)
 	}
+	var postAuthorIndexCount int
+	if err := conn.QueryRowContext(ctx, `
+SELECT count(*)
+FROM pg_indexes
+WHERE schemaname = current_schema()
+  AND tablename = 'posts'
+  AND indexname = 'idx_posts_author_created'`).Scan(&postAuthorIndexCount); err != nil {
+		t.Fatal(err)
+	}
+	if postAuthorIndexCount != 1 {
+		t.Fatalf("post author index count = %d, want 1", postAuthorIndexCount)
+	}
 	if _, err := conn.ExecContext(ctx, `
 INSERT INTO post_votes (user_id, post_id, value)
 VALUES ('homeowner', 'question-1', -1)`); err == nil {
@@ -276,6 +288,39 @@ INSERT INTO posts (
 		roots[0].UserVote != 1 {
 		t.Fatalf("root annotations = %+v", roots)
 	}
+	summary, err := queries.GetRootPostVoteSummary(ctx, sqlc.GetRootPostVoteSummaryParams{
+		ViewerID: "plumber",
+		RootID:   "question-1",
+	})
+	if err != nil || summary.Score != 2 || summary.UserVote != 1 {
+		t.Fatalf("root vote summary = %+v, %v", summary, err)
+	}
+	byAuthor, err := queries.ListRootPostsByAuthor(ctx, sqlc.ListRootPostsByAuthorParams{
+		AuthorID:    "homeowner",
+		HiddenState: string(PostStateHidden),
+		RowLimit:    50,
+	})
+	if err != nil || len(byAuthor) != 1 || byAuthor[0].ID != "question-1" {
+		t.Fatalf("roots by author = %+v, %v", byAuthor, err)
+	}
+	answeredBy, err := queries.ListRootPostsAnsweredBy(ctx, sqlc.ListRootPostsAnsweredByParams{
+		HiddenState: string(PostStateHidden),
+		AdminID:     "plumber",
+		RowLimit:    50,
+	})
+	if err != nil || len(answeredBy) != 1 || answeredBy[0].ID != "question-1" {
+		t.Fatalf("roots answered by admin = %+v, %v", answeredBy, err)
+	}
+	for _, state := range []PostState{PostStateLocked, PostStateVisible} {
+		n, err := queries.UpdateRootPostState(ctx, sqlc.UpdateRootPostStateParams{
+			PostState: string(state),
+			UpdatedAt: "2026-08-26T10:10:00Z",
+			ID:        "question-1",
+		})
+		if err != nil || n != 1 {
+			t.Fatalf("set root state %q rows=%d error=%v", state, n, err)
+		}
+	}
 
 	if _, err := conn.ExecContext(ctx, `
 DROP INDEX idx_posts_root_date;
@@ -413,7 +458,7 @@ WHERE schemaname = current_schema()
 func TestMigratePostsReportsStep(t *testing.T) {
 	t.Parallel()
 
-	exec := &failingMigrationExec{failAt: 5}
+	exec := &failingMigrationExec{failAt: 6}
 	err := migratePosts(context.Background(), exec)
 	if err == nil || !strings.Contains(err.Error(), "copy questions") {
 		t.Fatalf("error = %v, want copy questions context", err)