docs(agents): define repository workflow conventions

[tobyhede]

Summary

Define the repository-wide conventions used by agent skills for issue tracking,
triage labels, and domain documentation.

Changes

• Route active EQL work to cipherstash/stack rather than the historical EQL repository.
• Add the repository context map and initial EQL glossary.
• Document the multi-context domain/ADR layout used by domain-modeling workflows.
• Map canonical agent triage roles to this repository's GitHub labels.
• Add concise pointers from CLAUDE.md instead of inlining the reference material.

Scope

This PR contains only repository agent-workflow and domain-documentation
conventions. The EQL safe-reinstall ADR and implementation are stacked in
PR #961.

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[freshtonic]

Requesting changes on one two-minute item; everything else here is what I asked #961 to split out, done properly, and I'm glad to see it as its own deliberate decision.

The blocker: docs/agents/triage-labels.md maps roles to labels that don't exist. The table says these are "this repository's GitHub labels", but I checked the live label list: of the five, only wontfix exists — needs-triage, needs-info, ready-for-agent, and ready-for-human are not repo labels. An agent following this doc fails immediately (gh issue edit --add-label needs-triage errors on an unknown label). Since this PR's whole purpose is agent-facing conventions that are true, either create the four labels alongside the doc (gh label create ×4 — happy with any colours) or have the doc say they must be created on first use. Same class of note for the wayfinder:map / wayfinder:<type> labels in issue-tracker.md's Wayfinding section — those don't exist either; a one-line "create on first use" there covers it.

Verified clean:

• The repository-ownership routing (file EQL/protect-ffi work in cipherstash/stack, never the archived upstreams) is accurate, and it's correctly stated once in AGENTS.md for every agent and reinforced in packages/eql/AGENTS.md where the subtree's own docs would otherwise mislead.
• The split of concerns is right: universal facts land in AGENTS.md; Claude-specific skill-consumption glue is pointers in CLAUDE.md to docs/agents/*, keeping the "AGENTS.md is the single source of truth" contract intact rather than violating it the way the original in-#961 version did.
• docs/agents/domain.md is honest about lazy creation ("if these files do not exist, proceed silently; do not propose empty placeholders") — the example layout naming packages/stack/CONTEXT.md etc. is aspiration, and the doc says so. The docs/adr/ convention coexists sensibly with docs/plans/ (decisions vs designs); with this PR as its own decision point, my convention-by-fait-accompli objection on #961 is resolved.
• packages/eql/CONTEXT.md's glossary is genuinely good — the durable-domain / disposable-machinery / derived-index / non-reconstructable-dependency vocabulary is exactly the language #961's refusal messages need, and the Avoid lines will keep issue titles from drifting.
• No changeset is correct: nothing here ships in any tarball.
• CI green, including the EQL docs scans the new packages/eql/*.md files ride through.

Create (or caveat) the labels and this is an approve.

[freshtonic]

Approving. The blocker was resolved on the repository side, which is the better fix: all four triage labels (needs-triage, needs-info, ready-for-agent, ready-for-human) now exist on cipherstash/stack — verified against the live label list — and the wayfinding labels (wayfinder:map plus all four wayfinder:<type> values) were created too, which goes beyond what I asked and makes the issue-tracker doc's Wayfinding section true as written rather than caveated. The document set is unchanged from what I already verified (ownership routing accurate, AGENTS.md/CLAUDE.md split of concerns correct, honest lazy-creation language, solid EQL glossary, no changeset correctly). Every claim in these docs now checks out against the live repo. CI green.