Adds stable/next/pinned channel resolution so external/community modules
install at released git tags by default instead of tracking main HEAD.
Manifest now records channel, resolved version, and SHA per module for
reproducible installs.
CLI flags: --channel, --all-stable, --all-next, --next=CODE (repeatable),
--pin CODE=TAG (repeatable). Precedence: pin > next > channel > registry
default > stable. --yes accepts patch/minor upgrades but refuses majors.
Interactive "Ready to install (all stable)?" gate with a per-module
picker (stable/next/pin) when declined. Re-install prompts classify tag
diffs as patch/minor/major with semver-class-dependent defaults.
Legacy version:null manifests get a one-time migration prompt.
Custom modules gain an optional @<ref> URL suffix for pinning (https,
ssh, /tree/<ref>/subdir forms supported; local paths rejected).
Community modules honor --next/--pin overrides with a curator-bypass
warning; default path still enforces the approved SHA.
Quick-update now reads the manifest's recorded channel per module so
pinned installs don't silently roll forward.
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