Add clearer line-number evidence

[Shakargy]

Evidence currently cites files; pointing to the specific route/handler/line would make claims easier to audit and trust.

Suggested scope:

• Capture and surface start/end lines where the extractors already have them.
• Show line ranges in dtc explain and dtc evidence output.

What not to do yet: do not expand the concept ontology or change detection. This is presentation/precision of existing evidence, not new detection.

See PUBLIC_FEEDBACK_PLAN.md.