refactor: move buildable .NET source into src/, update CI/doc paths

Groups the repo root into src (buildable source), docs (already existed),
and everything else (db/, scripts/, tests/, deploy/ - deployment/ops/test
assets that aren't compiled, already organized as their own folders). CI
now only needs src/ to build: dotnet restore/build/test/publish all point
at src/TaxBaik.sln, src/TaxBaik.Web/, src/TaxBaik.Proxy/.

- git mv every project (Domain, Infrastructure, Application,
  Application.Tests, Web, Web.Client, Proxy) and TaxBaik.sln into src/ as a
  unit, so relative ProjectReference/.sln paths stay valid unchanged.
- .gitea/workflows/deploy.yml: 6 dotnet restore/clean/build/test/publish
  invocations now point at src/. db/migrations and scripts/ stay at root
  (deploy_gb.sh and browser-e2e.yml only touch published output and the
  deployed URL, not source paths - verified, no changes needed there).
- scripts/validate_admin_render.sh: admin render-mode file paths now
  src/TaxBaik.Web.Client/...
- scripts/validate_kst_timestamps.sh: dropped deploy.sh from its target
  list - that script was removed in the prior cleanup commit (dead, no
  CI workflow referenced it) but this validator still expected it to exist.
- CLAUDE.md, docs/ENGINEERING_HARNESS.md, docs/ADMIN_PATTERN_CRITIQUE_WBS.md:
  updated project-structure diagram, dotnet run/build commands, and grep
  targets to the new src/ paths (also fixed a pre-existing stale path in
  ADMIN_PATTERN_CRITIQUE_WBS.md that still said TaxBaik.Web/Components/Admin
  from before that ever moved to TaxBaik.Web.Client).
- Added a Repo Root harness rule + Architecture Guardrail entries: new files
  belong under src/docs/tests/scripts/db/deploy, not loose at root; temp
  work stays outside the repo (or under a gitignored .scratch/) and is
  never committed.

Verified locally: dotnet build/test src/TaxBaik.sln (26/26 tests), and all
three scripts/validate_*.sh pass against the new layout.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

CLAUDE.md

@@ -350,17 +350,18 @@ Repositories (데이터 계층)
 **단일 앱 구조** (공개 사이트 + 관리자까지 하나의 ASP.NET Core 앱):
 
 ```
-TaxBaik.Domain           클래스 라이브러리 (엔티티, 인터페이스, enum)
-TaxBaik.Infrastructure   클래스 라이브러리 (Dapper repository, DB 마이그레이션)
-TaxBaik.Application      클래스 라이브러리 (서비스, DTO, 비즈니스 로직)
-TaxBaik.Web              ASP.NET Core 앱 (포트 5001 - 서버는 순수 API)
-  ├─ Pages/             Razor Pages (공개 홈페이지, 블로그, 문의폼)
-  ├─ Components/
-  │  ├─ (Web pages)
-  │  └─ App.razor        Blazor Root (WebAssembly 렌더링)
-  └─ Services/          인증, 블로그, 문의 등 (API만 제공)
+src/                     빌드 가능한 .NET 소스 전체 (CI는 이 폴더만 빌드 대상으로 참조)
+  TaxBaik.Domain           클래스 라이브러리 (엔티티, 인터페이스, enum)
+  TaxBaik.Infrastructure   클래스 라이브러리 (Dapper repository, DB 마이그레이션)
+  TaxBaik.Application      클래스 라이브러리 (서비스, DTO, 비즈니스 로직)
+  TaxBaik.Web              ASP.NET Core 앱 (포트 5001 - 서버는 순수 API)
+    ├─ Pages/             Razor Pages (공개 홈페이지, 블로그, 문의폼)
+    ├─ Components/
+    │  ├─ (Web pages)
+    │  └─ App.razor        Blazor Root (WebAssembly 렌더링)
+    └─ Services/          인증, 블로그, 문의 등 (API만 제공)
 
-TaxBaik.Web.Client      (NEW) Blazor WebAssembly WASM 클라이언트
+  TaxBaik.Web.Client      (NEW) Blazor WebAssembly WASM 클라이언트
   ├─ _Imports.razor     네임스페이스 임포트
   └─ Components/
      └─ Admin/          관리자 페이지 (클라이언트 사이드)
@@ -460,7 +461,7 @@ ssh taxbaik-tunnel  # 터널 유지
 psql -h localhost -U taxbaik -d taxbaikdb -c "\dt"
 
 # 또는 .NET 앱 실행 (자동으로 마이그레이션 실행)
-dotnet run -p TaxBaik.Web
+dotnet run -p src/TaxBaik.Web
 ```
 
 #### 단계 3: 개발 워크플로우 (단일 앱 통합)
@@ -470,7 +471,7 @@ dotnet run -p TaxBaik.Web
 ssh -L 5432:127.0.0.1:5432 kjh2064@178.104.200.7
 
 # 터미널 2: 통합 Web 앱 (Razor Pages + Blazor Server Admin)
-cd TaxBaik.Web
+cd src/TaxBaik.Web
 dotnet run
 # 접속:
 #   - 홈페이지: http://localhost:5001/taxbaik
@@ -1762,7 +1763,7 @@ public interface INtsApiClient
 
 ### 빌드
 ```bash
-dotnet build TaxBaik.sln
+dotnet build src/TaxBaik.sln
 ```
 
 ### 서버 상태 확인 (SSH)
@@ -2166,7 +2167,7 @@ else
 | 11/15 ~ 11/30 | 종합부동산세 납부 | `comprehensive-real-estate-tax` | real-estate-tax |
 | 12/1 ~ 12/31 | 연말 증여·절세 플래닝 | `year-end-gift` | family-asset |
 
-캘린더 정의 위치: `TaxBaik.Application/Seasonal/TaxSeasonCalendar.cs`
+캘린더 정의 위치: `src/TaxBaik.Application/Seasonal/TaxSeasonCalendar.cs`
 
 시즌 추가/수정은 이 파일만 변경하면 된다. DB·마이그레이션 변경 없음.