Retire the shared project tag value from the coverage report

[ale210]

Retires the project: shared tag value from -ProjectTag, following the reversal of decision 2 of DR-Machine-to-machine-IAM-scoping on 2026-09-12. A resource belonging to no single project now carries no project tag at all. The wiki record was updated in the same pass (devops.wiki commit ecbf3dc), with decision 2's original text and reasoning struck through rather than deleted.

This is not just a deleted bucket, and that is the part worth reviewing. Removing shared on its own would have pushed every shared resource into missing, turning correct state into a false-positive defect list. So missing is renamed untagged, and both the code and scripts/README.md now say plainly that the bucket mixes two cases the script cannot separate:

• a resource that belongs to no single project — correct, and it wants no tag
• a resource nobody has classified yet — a real gap

Telling them apart is a judgement per resource type, not something the report can do. That ambiguity is the genuine cost of retiring the value and it was accepted deliberately; decision 2 had existed to avoid it.

A literal shared value, should one ever appear, now falls through to nonconforming rather than being recognised. That is intended and is commented where the known-values list is defined, so it does not get "fixed" back.

Verification. Run against 035866691871 on this branch: 77 conforming, 4 nonconforming, 24 untagged, 73.3%. The nonconforming four are the civic-tech-index SSM parameters tracked by hackforla/incubator#217, so the bucket that predicts an outage still reports truthfully. The 24 untagged are the case above in miniature — the 4 shared S3 buckets (Terraform state, CloudTrail logs) are correctly untagged, while the 10 ECS task roles are a real gap tracked by hackforla/incubator#199.

Nothing was tagged project=shared live — checked both regions plus the two IAM roles the tagging API cannot see. The DR was adopted 2026-09-01 but that decision was never implemented, so no resource changes state as a result of this and there is no untagging work.

No issue: this follows directly from the standard changing.