fix!: align generated marketplace names

[mishamilovidov]

Summary

Use one generated marketplace name across supported clients and document the Codex native migration.

Changes

• Set dotagents as the shared name for generated Claude Code, GitHub Copilot, Cursor, and Codex marketplaces.
• Add project and global Codex registration, availability, installation, and enablement proof.
• Update docs, QA references, and release notes for <name>@dotagents and the required Codex migration.
• Merge upstream main through #194, retain the two-argument Copilot pathMarketplace call, and update native QA for Copilot CLI 1.0.88 output.

Testing

• pnpm check on the current host (1,139 tests: 295 in dotagents-lib and 844 in dotagents; lint and typecheck passed).
• pnpm --dir docs build on the current host (0 errors, 0 warnings, 5 pages).
• pnpm qa:example on the current host (install-files and sync-repair passed).
• pnpm qa:plugins on the current host (Claude, Copilot CLI 1.0.88, and Codex native no-auth workflows passed; Grok CLI unavailable).
• Non-root Docker validation of this head passed on Node 24.21.0 with frozen root and docs installs, pnpm check, docs build (5 pages), pnpm qa:example, and pnpm qa:plugins (Claude Code 2.1.284, Copilot CLI 1.0.89, Codex CLI 0.159.0). The container used isolated agent homes, a read-only source mount, and no host credentials or model-backed invocation.

Related Issues

• Follow-up to #113
• Closes #175
• Incorporates #166
• Relates to #176

Notes

#173 merged as 517964b. #166 merged as 60254b3, and #182 merged as de189d6. This branch first merged all three as 9d00ab7, then landed the Copilot pathMarketplace call-site correction as its own signed commit 11890fd, and merged upstream main again (the 3.1.0 release) as 7b8a04b. That merge keeps this branch's Unreleased breaking-change migration notes ahead of the 3.1.0 changelog entry and preserves the Codex env_http_headers fix from #173. main then added #185 (nested Pi plugin skill discovery), removed its CLAUDE.md symlink in #189, and restricted skill adoption to directories with SKILL.md in #194. This branch merged the latest main as a8689b5 and adjusted the Copilot QA to CLI 1.0.88 in fccd132.

Merge last, after #178. After that PR merges, rebase or merge the latest main again if it has moved, and confirm the shared marketplace name and activation docs still line up.

Remaining merge order: #178 → #177.

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