Add .katalystignore to store user preferences

[marutilai]

• In katalyst_core/utils/file_utils.py, create a new function load_katalyst_ignore() that reads a .katalystignore file from the .katalyst folder at the project root.
• This gives the user fine-grained control over what the agent can see, separate from their .gitignore
• Update should_ignore_path to check against both the hardcoded KATALYST_IGNORE_PATTERNS and the patterns from this new file.

Content of .katalystignore

• This file allows the user to specify project-specific files and directories that the agent should not touch. It gives the user control and peace of mind.
• it protects user's project-specific data and logic.
• A user might have large data files (data/), secret keys (*.pem), or generated documentation (docs/build/) that they don't want the agent to waste tokens on or accidentally modify.
• implement /ignore command to let user define what they want to ignore. /ignore will open the .katalystignore file which user can edit and save

Sample content for .katalystignore

# .katalystignore
#
# This file tells the Katalyst Agent which files and directories to ignore.
# The syntax is the same as .gitignore.
#
# Use this to prevent the agent from accessing sensitive files, large data sets,
# or irrelevant build artifacts.

#
# Sensitive Files and Secrets
#
# Although .env is already ignored by default, add any other secret files here.
*.key
*.pem
credentials.json
secrets.yml

#
# Large Data Files
#
# Prevent the agent from reading large data sets that would consume the context window.
data/
*.csv
*.jsonl
*.parquet
*.db
*.sqlite

#
# Test Outputs and Reports
#
# From your directory structure, these seem relevant to ignore.
test_outputs/
test_reports/
__snapshots__/
htmlcov/
.coverage

#
# Documentation & Assets
#
# Ignore these if you want the agent to focus only on source code.
docs/
assets/
images/

#
# Third-Party / Vendored Code
#
vendor/
third_party/

#
# Generated Code
#
# Add directories or files for code generated by other tools that the
# agent should not modify.
# e.g., generated/
# e.g., *.pb.go