fix(config,extension): BRAIN_PATH 빈문자열 버그 + 크로스프로젝트 DEDUP MERGE 수정

- config.py: os.getenv BRAIN_PATH 빈값 시 CWD 해석 → or 패턴으로 수정
- extension.ts: writePendingApproval DEDUP에 project_name 가드 3곳 추가
- extension.ts: HTTP /pending file_permission dedup에도 project_name 가드
- known-issues: 2건 추가 (BRAIN_PATH, DEDUP MERGE)
- devlog: 2026-03-11 생성

config.py

@@ -16,10 +16,11 @@ class Config:
     DISCORD_GUILD_ID: int = int(os.getenv("DISCORD_GUILD_ID") or "0")
 
     # Antigravity Brain path
-    BRAIN_PATH: Path = Path(os.getenv(
-        "BRAIN_PATH",
-        os.path.expanduser("~/.gemini/antigravity/brain")
-    ))
+    # NOTE: os.getenv returns "" (not None) when .env has BRAIN_PATH= (empty value).
+    # Path("") resolves to "." (CWD), which is WRONG. Use `or` to handle both None and "".
+    BRAIN_PATH: Path = Path(
+        os.getenv("BRAIN_PATH") or os.path.expanduser("~/.gemini/antigravity/brain")
+    )
 
     # Watcher settings
     DEBOUNCE_SECONDS: float = float(os.getenv("DEBOUNCE_SECONDS", "5"))