Introduces the kernel lifecycle and migrates the first real page to the
feature-module contract:
- kernel/lifecycle.js: MountContext (loadScripts/loadFragment/setContent
+ an AbortController/unsub teardown ledger so mounts can't leak
listeners or live streams).
- features/backup/index.js: Backup Center as a self-contained module
(LP.features.register with mount/unmount); heavy backup-page.js stays
lazy-loaded on first mount.
- spa.js: routes whose feature has a registered mount() are driven
through the kernel; everything else still uses its legacy handleX().
navigate() unmounts the current feature first. Both fall back to the
legacy handler if a module is missing or mount throws.
Strangler step: /backup now flows manifest -> registry -> mount/unmount.
The other pages are untouched. handleBackup remains as the fallback.
Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
Signed-off-by: librelad <librelad@digitalangels.vip>
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