argos-dev: create-ticket skill and pointers for the new issue templates

[bracyw]

Argos is moving to four issue templates (idea, spike, epic, dev work) and a new label set (Argos #812), and its AI context is moving out of the repo (Argos #810). This updates the Argos workspaces and defaults to match.

• create-ticket skill: picks the template, reads it from the repo, drafts the body with the web form's headings, picks written-by and area labels, and files after the user OKs it. file-ticket.sh sets the issue type, assigns the user, links the sub-issue, and stops if a label is missing. The templates' field descriptions carry the guidance, so the skill stays short.
• github.sh: gh_init also takes an owner/name repo, so skills can target repos outside the workspace (Nero-2.0).
• docs/CONTEXT.md (argos-dev, experimental): a short Conventions section with the few project-specific rules from the deleted angular-client and scylla-server CLAUDE.md files, plus ADR naming. The rest was Angular and Rust defaults and is dropped. The stale pointer to the workflow glossary is gone.
• CLAUDE.md (argos-dev, experimental, defaults): conventions and ADR naming point to docs/CONTEXT.md; the issue tracker points to Argos's issue-tracker.md (and create-ticket in argos-dev). No more pointers to files #810 deletes.
• log-future-addition: points to create-ticket instead of the old conventions, and uses the new written-by and area labels.

create-ticket can't file until #812 merges and the new labels exist. ci/check.sh passes.