refactor(host-monitor): rename plugin identity

[MateoCerquetella]

Summary

• rename the active plugin identity from machine-monitor to host-monitor across the directory, package, collection, routes/RPC ids, CSS/keyframes, tests, docs, lockfile, and living repository context
• preserve the readable product name Host Monitor and ordinary “machine” terminology for monitored resources
• add an active-source regression guard so the retired compound id cannot return unnoticed
• preserve the immutable legacy tag and completed historical evidence without shipping an alias or second sampler

UI

The product UI is intentionally unchanged; only its technical identity moves.

Processes and floating monitor

Existing installations

BB treats the new package id as a separate plugin. An installation under the retired id cannot update across the rename; remove the earlier Host Monitor entry, install host-monitor, and reapply threshold settings. The local development install was migrated with its existing true / 70 / 85 values and verified with exactly one running sampler.

Verification

• derived id: host-monitor
• focused Host Monitor check: SDK declarations, TypeScript, 145/145 tests, server/app/host build
• root npm run check: all three workspaces pass
• server/app/host metadata: plugin host-monitor, BB 0.40.0, SDK 0.4.21
• package dry-run: bb-plugin-host-monitor@0.1.0, 37 expected files
• active product/repository scan: zero retired compound-id matches outside historical migration records
• live BB: 4/4 hosts, preserved 70/85 thresholds, cards/rows, masked inspector, process search/sort, outside-click sidebar dismissal, keyboard-movable floating monitor, and no old request/asset/class path
• retired route: normal unavailable panel, no redirect
• independent security, UI/UX, diff, and final code review: no product blocker
• independent clean-main capability replay and root verification: pass
• git diff --check: pass

Release invariants

• proposed new tag: host-monitor/v0.1.0 at 04fc439cc69d76f78bb6bb1f853e421a1b9e90a0
• legacy machine-monitor/v0.1.0 remains untouched and still peels to 9db09cc35553493113f31e5352a44911ae92bc73
• package remains private/Git-only; no npm publication
• marketplace PR #128 will be updated in place to the new entry after the public tag is verified

Ready for review; this PR must not be merged automatically.