Make docs qualification consume reachability failures from section captures

[rmcdaniel]

Problem

Commit f62fa8d34f0ab13e2d5b4ca999047b28aba3f78f required rendered evidence focused on the changed #public-manifests state. The commit landed, but an exact live capture of that state exits unsuccessfully with a non-empty geometry.unreachable_controls report at every required viewport class.

The reachability collector is working; the missing protection is in change classification or evidence consumption. Screenshots showing the changed row were accepted without ensuring the associated reachability result was successful for the exact landed revision.

Acceptance criteria

• Customer-facing documentation changes that require a section-focused rendered state cannot satisfy qualification with screenshots alone; the corresponding machine report and capture exit status are required.
• Any non-empty geometry.unreachable_controls result fails qualification at desktop, intermediate, mobile, and short-height viewports.
• Evidence is bound to the exact candidate commit and required interaction or scroll state, so evidence from an earlier revision or a default first viewport cannot satisfy the check.
• A regression fixture representing an interactive disclosure partially occluded by sticky navigation proves the qualification path rejects the evidence.
• The corrected live Platform Conformance #public-manifests state passes the same qualification matrix without weakening overflow, clipping, console, or page-error checks.

Delete when

Delete when the negative fixture is rejected end to end and an exact-revision section-focused evidence matrix cannot be accepted while any required reachability report is failing.