Sweep remove.rs and repair.rs (#1875)

* Start sweep of remove.rs and repair.rs

Assisted-by: Claude Code:claude-opus-5-5

* Sweep repair.rs: drop the noun parameter

The human formatters took an ArtifactNoun that production always
passed as BLOB; they now use BLOB directly. Envelopes print through
ui::print_json. Trims history comments and bare issue numbers.

Tests: drops the tautological HOSTED_ONLY_REASON assert, the two
multibyte runs that format_id_list's own test already covers, and
merges the two offline no-download tests into one that covers dry
run and wet run.

Assisted-by: Claude Code:claude-opus-5-5

* Sweep remove.rs: inline wrappers, dedupe tails

Inlines emit_not_found and hosted_unwind_error, and replaces the
HostedUnwindError newtype with a String. The hosted_reverted event and
the kept-entries exit tail are each built by one helper instead of
twice. print_hosted_leg_warnings becomes print_run_warnings, since it
also prints the rollback's warnings. Envelopes print through
ui::print_json and warnings use RunWarning::new. Output is unchanged.

Tests: deletes dry_run_footer_matches_repair, which compared a
constant to its own literal, and asserts the not-installed warning's
exact lines instead of fragments.

Assisted-by: Claude Code:claude-opus-5-5

* Apply review cleanups to the remove/repair sweep

The hosted-only path records its events directly with the hosted mode
instead of collecting and tagging them, and stops cloning the leg's
warnings. Repair's hosted-only print says why it adds a period.

Assisted-by: Claude Code:claude-opus-5-5

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Co-authored-by: Claude <noreply@anthropic.com>

Author: mikolalysenko