chore(agents): consolidate agent context and compress instruction files (#5195)

* chore(agents): consolidate agent context and compress instruction files

Replace AGENT.md and .cursor/rules with a single AGENTS.md entry point plus
CODEMAP.md, and cut duplicated guidance out of the instruction files.

The same six non-negotiables were restated across seven files, so editing one
.tsx under packages/ loaded ~36.8KB of instructions to say them four times
over. Now ~28.7KB: generic React/Vitest material dropped, Fusion-specific
patterns kept.

Also corrects rules that were actively wrong:
- vite plugins were documented as `fusion-framework-vite-plugin-*`; every one
  of them is `@equinor/`-scoped
- the documented pre-PR gate `pnpm -w check` runs biome only, silently
  skipping fusion-lint; now `pnpm lint`
- documentation.instructions.md applied to `**/*.md`, firing its
  retrieval-corpus rules on changesets and agent files

Adds `pnpm verify:agent-context` plus a CI job so CODEMAP.md cannot drift from
the real workspace, and contributing/fusion-lint.md for lint knowledge that
previously lived only in agent memory.

No changeset: nothing under packages/* or cookbooks/* is touched.

* ci: stop double-running copilot setup steps on same-repo PRs

* docs(codemap): fully qualify every package path

The package map listed paths relative to `packages/` (`modules/http`), relying
on the section heading for context. The CLI/tooling table mixed both styles in
adjacent rows.

Fully qualifying them also brings all ~50 paths under the existence check in
verify-agent-context.mjs, which only inspects `packages/...` and `cookbooks/...`
strings. They were previously invisible to CI; a typo now fails the build.

* docs: use pnpm instead of npx/npm in documented commands

The repo's own non-negotiable is "pnpm only", but three documented commands
used `npx vitest` or `npm view`.

Verified both replacements work: `pnpm exec vitest run --project '*lint-core*'`
runs 30 tests, `pnpm view <pkg> version` returns from the registry.

Also corrects the project filter placeholder. Vitest project names are
`<package-name>@<version>`, so a bare `'<name>'` never matches — it needs a glob.

Author: odinr