Add explicit authoring constraint in filter-rule-engine-usage.md:
all drop rules must set stop_on_match=true to prevent low-priority
drop rules from overriding high-priority keep decisions.
Eliminate the NamedTemporaryFile workaround in server.py by adding a
`context` dict parameter to run_freshrss_pipeline. The pipeline resolves
filter context from the dict first, falling back to context_path, then
defaulting to an empty FilterContext. Remove unused json/tempfile imports.
Added explanatory comments to server.py, freshrss_pipeline.py, pipeline.py,
freshrss.py, keyword_index.py, summary_loop.py, and filters/engine.py.
Also added CODE_REVIEW.md with prioritized improvement suggestions.
wdm