Remove dead ttl_behavior field from ContextPolicy

[Copilot]

Summary

Closes #65

ContextPolicy.ttl_behavior was configurable but never read — ContextItem has no TTL field and no pipeline stage acts on it. Silently ignored config erodes trust; removed it until TTL support is implemented (tracked separately in #67).

Changes

• config.py — Remove ttl_behavior: str = "drop" field and its docstring entry from ContextPolicy
• __main__.py — Drop ttl_behavior from the _cmd_init scaffold config JSON
• tests/test_config.py — Remove assertion on the now-absent field

Checklist

• Tests added or updated for every new/changed public function
• make ci passes locally (fmt + lint + type + test + example + demo)
• CHANGELOG.md updated under ## [Unreleased]
• Docstrings added for all new public APIs (Google-style)
• Every modified module stays ≤ 300 lines (or a decomposition issue is linked above)
• Related issue linked in the summary above
• Agent-facing docs updated if pipeline, API, or conventions changed

Notes for reviewers

sensitivity_floor, sensitivity_action, and redaction_hooks are not touched — those are already wired into context/sensitivity.py as of v0.1.2. Only ttl_behavior is removed here.

[Copilot]

Pull request overview

Removes the unused ContextPolicy.ttl_behavior configuration surface to avoid silently ignored settings until real TTL/eviction support is implemented (tracked in #67).

Changes:

• Removed ttl_behavior from ContextPolicy (and its docstring entry).
• Updated the CLI init scaffolded contextweaver.json to no longer emit ttl_behavior.
• Updated config tests to stop asserting the removed default.

Reviewed changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated 1 comment.

File	Description
src/contextweaver/config.py	Removes the dead ttl_behavior field and related docstring text from ContextPolicy.
src/contextweaver/__main__.py	Updates the init command’s scaffold config JSON to omit ttl_behavior.
tests/test_config.py	Removes the assertion tied to the deleted ttl_behavior default.