fix(privacy): avoid replacing bare values in prose

[ranxi2001]

Description

Prevent skill privacy placeholderization from rewriting configured bare values
that merely appear at the start of ordinary prose after a colon or equals sign.
Bare assignments now match only when the configured value is followed by
optional horizontal whitespace and then LF, CRLF, or end of input. Quoted-value
replacement behavior and the placeholder format remain unchanged.

Human Involvement

• A human participated in the implementation or review loop
• This PR was generated entirely by AI agents without human participation in the loop

Related Issue

Fixes #3791

Type of Change

• Bug fix (non-breaking change that fixes an issue)
• New feature (non-breaking change that adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• Documentation update
• Refactoring (no functional changes)
• Performance improvement
• Test update

Changes Made

• Anchor unquoted colon/equal assignment values to line boundaries with an escaped pattern.
• Preserve separators, leading/trailing horizontal whitespace, and LF/CRLF endings.
• Add regression coverage for prose, CRLF, regex-special values, and quoted-value compatibility.

Testing

• I have added tests that prove my fix is effective or that my feature works
• New and existing focused unit tests pass locally with my changes
• I have tested this on the following platforms:
  • Linux
  • macOS
  • Windows

Commands run:

python -m pytest -o addopts='' tests/server/test_privacy_config_service.py -k placeholderization -q
python -m ruff format --check openviking/privacy/skill_placeholder.py tests/server/test_privacy_config_service.py
python -m ruff check openviking/privacy/skill_placeholder.py tests/server/test_privacy_config_service.py
python -m mypy --follow-imports=skip --ignore-missing-imports openviking/privacy/skill_placeholder.py
python -m compileall -q openviking/privacy/skill_placeholder.py tests/server/test_privacy_config_service.py
git diff --check upstream/main...HEAD

Checklist

• My code follows the project's coding style
• I have performed a self-review of my code
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation
• My changes generate no new warnings
• Any dependent changes have been merged and published

Screenshots (if applicable)

Not applicable.

Additional Notes

The focused helper tests report 5 passed with four pre-existing Pydantic
deprecation warnings. The complete privacy service module was attempted, but
service-level cases require the unavailable ragfs_python native binding and
one existing extraction case invokes configured VLM I/O. make check-deps
stops because CMake is absent on this host. No native code is changed by this PR.