feat(skills): port Matt Pocock's skills as plugin skills and drop the dependency

[gborges0727]

Ports thirteen of Matt Pocock's skills into the plugin as first-class skills, rewritten in plain English, and removes the mattpocock-skills dependency.

Skills added

• grill merges grilling, grill-me, and grill-with-docs. It runs domain-modeling alongside when the repo has a CONTEXT.md.
• build merges implement, tdd, and implement-spec. It takes the conversation as the ask by default and decides which public functions get tests without a confirm step. It reviews the diff against the ask through opus-medium, with the repo's own review instructions winning, and commits only when told. A spec with tickets fans out one worktree per ticket.
• spec merges to-spec and to-tickets. It writes a trimmed spec and offers tickets only when the work will not fit one session.
• routine is loop-me under a name that does not collide with the built-in /loop.
• wayfinder keeps the map, decisions, unresolved questions, and out-of-scope sections as files, at a third of the length, with the claim and assignee rules cut.
• handoff merges handoff and claude-handoff and writes under docs/handoff/ or into Bear, never the temp directory.
• research, wait-what, teach, writing-for-agents, domain-modeling, diagnosing-bugs, and resolving-merge-conflicts are rewritten from their upstream bodies. teach publishes lessons as Claude artifacts. writing-for-agents drops the leading-words section and states the positive-form rule instead.

Where documents go

reference/output-locations.md holds the one rule. A repo can carry .claude/gborges-standard.json with docs and tracker keys, written by the new /setup-repo command and scripts/setup-repo.sh. Without it, everything goes under docs/ and nothing touches GitHub unless asked.

Codex

The ten user-only skills, pair-debate and model-routing-review included, get agents/openai.yaml with allow_implicit_invocation: false, since Codex ignores the disable-model-invocation frontmatter.

Also in this PR

• "The file is the signal" joins the banned mottos in the style, in RULES.md, and in check.py.
• .claude/skills/upstream-check/ is a repo-only skill that lists what changed upstream since commit 3cca18b.
• The README table has a row per new skill and credits the upstream repo.
• Both plugin versions move to 1.30.0 and the rev to 36.

A machine with the mattpocock plugin still installed at user scope will list two skills for each shared name until it is uninstalled.