feat: implement 8 OpenSpec proposals for security, reliability, and UX improvements

## Security Enhancements (P0)
- Add input validation with max_length and numeric range constraints
- Implement WebSocket token authentication via first message
- Add path traversal prevention in file storage service

## Permission Enhancements (P0)
- Add project member management for cross-department access
- Implement is_department_manager flag for workload visibility

## Cycle Detection (P0)
- Add DFS-based cycle detection for task dependencies
- Add formula field circular reference detection
- Display user-friendly cycle path visualization

## Concurrency & Reliability (P1)
- Implement optimistic locking with version field (409 Conflict on mismatch)
- Add trigger retry mechanism with exponential backoff (1s, 2s, 4s)
- Implement cascade restore for soft-deleted tasks

## Rate Limiting (P1)
- Add tiered rate limits: standard (60/min), sensitive (20/min), heavy (5/min)
- Apply rate limits to tasks, reports, attachments, and comments

## Frontend Improvements (P1)
- Add responsive sidebar with hamburger menu for mobile
- Improve touch-friendly UI with proper tap target sizes
- Complete i18n translations for all components

## Backend Reliability (P2)
- Configure database connection pool (size=10, overflow=20)
- Add Redis fallback mechanism with message queue
- Add blocker check before task deletion

## API Enhancements (P3)
- Add standardized response wrapper utility
- Add /health/ready and /health/live endpoints
- Implement project templates with status/field copying

## Tests Added
- test_input_validation.py - Schema and path traversal tests
- test_concurrency_reliability.py - Optimistic locking and retry tests
- test_backend_reliability.py - Connection pool and Redis tests
- test_api_enhancements.py - Health check and template tests

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

backend/app/schemas/project.py

@@ -1,4 +1,4 @@
-from pydantic import BaseModel
+from pydantic import BaseModel, Field
 from typing import Optional
 from datetime import datetime, date
 from decimal import Decimal
@@ -12,9 +12,9 @@ class SecurityLevel(str, Enum):
 
 
 class ProjectBase(BaseModel):
-    title: str
-    description: Optional[str] = None
-    budget: Optional[Decimal] = None
+    title: str = Field(..., min_length=1, max_length=500)
+    description: Optional[str] = Field(None, max_length=10000)
+    budget: Optional[Decimal] = Field(None, ge=0, le=99999999999)
     start_date: Optional[date] = None
     end_date: Optional[date] = None
     security_level: SecurityLevel = SecurityLevel.DEPARTMENT
@@ -25,13 +25,13 @@ class ProjectCreate(ProjectBase):
 
 
 class ProjectUpdate(BaseModel):
-    title: Optional[str] = None
-    description: Optional[str] = None
-    budget: Optional[Decimal] = None
+    title: Optional[str] = Field(None, min_length=1, max_length=500)
+    description: Optional[str] = Field(None, max_length=10000)
+    budget: Optional[Decimal] = Field(None, ge=0, le=99999999999)
     start_date: Optional[date] = None
     end_date: Optional[date] = None
     security_level: Optional[SecurityLevel] = None
-    status: Optional[str] = None
+    status: Optional[str] = Field(None, max_length=50)
     department_id: Optional[str] = None