filter(npm): add npm install / npm ci filter

[mpecan]

Goal

Expand npm filters to cover npm install and npm ci — the install operations. Currently npm/run.toml exists for script execution but install operations have no filter.

Background

npm install with a medium-sized project emits:

• npm warn deprecated <package>@<version>: ... for every deprecated transitive dependency (often dozens of lines for packages the user can't control)
• npm notice informational lines
• Progress indicators (in non-CI mode)

The community has requested a way to suppress deprecated warnings from sub-dependencies while keeping those from direct dependencies (npm/cli#5232). Currently the only option is --loglevel=error which also hides useful notices.

Filters to Add

npm/install.toml — npm install / npm i

• Skip: npm warn deprecated lines (transitive dep deprecations), npm notice lines, progress lines
• Keep: npm error lines, npm warn EBADENGINE (Node version mismatch), security audit summary if present, the final added X packages summary line

npm/ci.toml — npm ci

• Same as npm/install.toml but also keep npm warn lines that indicate lock file conflicts (these are actionable in CI context)

Fixture Files Needed

• tests/fixtures/npm/install-clean.txt — fresh install with many deprecated transitive dep warnings
• tests/fixtures/npm/install-error.txt — install failure (version conflict, network error)
• tests/fixtures/npm/ci-lockfile-mismatch.txt — npm ci with lock file mismatch warning

Acceptance Criteria

• Deprecated transitive dependency warnings removed from output
• npm error lines always preserved
• Final package count summary line always preserved
• Integration tests pass for all fixture files