docs - add RFC 027-041 roadmap drafts

[dannymeijer]

Summary

This PR adds the draft RFC roadmap for InQL's next future-scope RFC batch. It introduces RFC 027 as the relational evidence umbrella and adds child RFC drafts for semantic identity, metadata attachments, Prism lineage, inspection artifacts, execution observations, adapter coverage, quality observations, governed attributes, governed plan bundles, plan diffs, evidence exchange bridges, interoperability profiles, and Prism ingress/frontends. It also includes RFC 039 for the pandas-familiar exploration API so the RFC corpus remains continuous through RFC 041.

Each RFC now has one dedicated tracker issue: #61-#75.

Type of change

• Bug fix
• New feature
• Refactor / maintenance
• Documentation
• CI / tooling
• RFC (adds/updates docs/rfcs/*)

Area(s)

Select the primary areas touched (labels sync from checked lines when the triage workflow runs):

• Package & tests
• Specification (RFCs)
• Documentation
• Automation & repo config
• Other

Key details

• User-facing behavior: no runtime/library behavior changes. This is a draft RFC batch that records future scope for lineage, governance evidence, observations, interoperability semantics, external plan ingress, transformation-project evidence exchange, and pandas-familiar exploration ergonomics.
• Internals: no implementation changes. The RFC index now lists RFC 027-041 as Draft while preserving current main statuses for already-implemented RFCs.
• Tracking: RFC 027-041 are linked to InQL issues RFC 027: Relational evidence program #61-RFC 041: Prism plan ingress and external client frontends #75 in their RFC headers, and all point back to this RFC PR.
• Risks: the batch is broad and should be reviewed as roadmap/north-star scope, not as committed implementation order. RFC 039 is included as a draft spec only; the separate spike/prism-ingress-rfc039 branch still preserves implementation-spike code and is not part of this PR.

Testing / verification

• make ci (or make fmt-check, make build, make test)
• Manual verification described below

Manual verification notes:

• git diff --cached --check passed before each commit.
• git diff --check passed before push.
• Verified the RFC index preserves current main statuses for already-implemented RFCs and only adds the new draft RFC rows/links.
• Checked existing InQL issues before creating trackers; the only prior hit was an unrelated future-scope mention in an older RFC012 issue, not a dedicated RFC 040 tracker.
• Scanned the migration/evidence-exchange RFC additions for public-safety wording; they use representative ecosystem lists across SQL engines, cloud/lakehouse engines, catalogs, transformation projects, orchestrators, lineage tools, and quality tools rather than customer-specific context.

Docs impact

• No docs changes needed
• Docs updated
• Docs follow Divio intent (tutorial/how-to/reference/explanation) where applicable

If docs updated:

• Link(s): docs/rfcs/027_relational_evidence_program.md, docs/rfcs/028_semantic_identity_targets.md, docs/rfcs/029_metadata_attachments.md, docs/rfcs/030_prism_lineage_graph.md, docs/rfcs/031_inspection_artifacts.md, docs/rfcs/032_execution_observations.md, docs/rfcs/033_adapter_requirements_coverage.md, docs/rfcs/034_quality_assertions_observations.md, docs/rfcs/035_governed_attributes_policy_checkpoints.md, docs/rfcs/036_governed_plan_bundle.md, docs/rfcs/037_plan_diff_blast_radius_inputs.md, docs/rfcs/038_evidence_exchange_bridges.md, docs/rfcs/039_pandas_familiar_exploration_api.md, docs/rfcs/040_interoperability_semantic_profiles.md, docs/rfcs/041_prism_plan_ingress_frontends.md, docs/rfcs/README.md

Checklist

• I kept public docs user-focused and moved internals to contributing docs when appropriate
• I avoided duplicating canonical install/run instructions in multiple places
• I added/updated tests where it materially reduces regressions