fix(gitea-mcp): address MCP tool issues from Sprint 6

Fixes #281 - Multiple MCP tool issues discovered during sprint execution

## Changes

1. **list_issues Token Overflow** (Issue 1)
   - Added `milestone` parameter to filter issues server-side
   - Reduces response size by filtering at API level instead of client-side

2. **Type Coercion for MCP Serialization** (Issues 2 & 4)
   - Added `_coerce_types()` helper function in server.py
   - Handles integers passed as strings (milestone_id, issue_number, etc.)
   - Handles arrays passed as JSON strings (labels, tags, etc.)
   - Applied to all tool calls automatically

3. **Sprint Approval Check Clarification** (Issue 3)
   - Updated sprint-start.md to clarify approval is RECOMMENDED, not enforced
   - Changed STOP/block language to WARN/suggest language
   - Added note explaining this is workflow guidance, not code-enforced

## Files Changed
- mcp-servers/gitea/mcp_server/gitea_client.py: Added milestone param
- mcp-servers/gitea/mcp_server/tools/issues.py: Pass milestone param
- mcp-servers/gitea/mcp_server/server.py: Type coercion + milestone schema
- plugins/projman/commands/sprint-start.md: Clarified approval check

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

mcp-servers/gitea/mcp_server/tools/issues.py

@@ -98,6 +98,7 @@ class IssueTools:
         self,
         state: str = 'open',
         labels: Optional[List[str]] = None,
+        milestone: Optional[str] = None,
         repo: Optional[str] = None
     ) -> List[Dict]:
         """
@@ -106,6 +107,7 @@ class IssueTools:
         Args:
             state: Issue state (open, closed, all)
             labels: Filter by labels
+            milestone: Filter by milestone title (exact match)
             repo: Override configured repo (for PMO multi-repo)
 
         Returns:
@@ -124,7 +126,7 @@ class IssueTools:
         loop = asyncio.get_event_loop()
         return await loop.run_in_executor(
             None,
-            lambda: self.gitea.list_issues(state, labels, repo)
+            lambda: self.gitea.list_issues(state, labels, milestone, repo)
         )
 
     async def get_issue(