Feature Request: Project-scoped knowledge base ignore/filter file

**Note:** This feature request is for Kiro CLI (successor to Amazon Q CLI).

Currently, knowledge bases are user-scoped and visible across all projects/workspaces. When working on multiple projects, knowledge indexed for Project A appears in Project B's context, causing potential cross-contamination.

**Problem:**
- No way to exclude specific knowledge bases from a project without deleting them
- Deletion destroys indexed data needed in other projects
- Re-indexing is time-consuming for large codebases

**Proposed Solution:**
Add support for a `.kiro/knowledge_ignore` file (or similar) that specifies which knowledge bases to exclude from the current workspace context.

Example:
```
# Pattern-based filtering
asterix*
legacy-project*

# Or by context ID
# id:f2137f6b-1939-493f-94e7-ac70a81b42fd
```

**Benefits:**
- Non-destructive - preserves indexed data globally
- Project-scoped rules
- Simple pattern matching
- Prevents accidental context mixing between unrelated projects

**Alternatives Considered:**
- Agent-specific knowledge bases (exists but doesn't solve cross-project issue within same agent)
- Manual deletion (destructive, requires re-indexing)