fix(cli): name --override-stale-lock on the top-level adopt help line

[arcaven]

When adopt refuses on a recent burst log, its hint says to pass --override-stale-lock, but the top-level help line for adopt does not list that flag, so a user checking help cannot confirm it exists. Adding it to the line makes the help match what adopt accepts (cmd/sideshow/adopt.go:13) and what the top-level disable line and the per-verb enable help already show.

Item 3 of #95 only. Items 1 and 2 are out of scope: item 1 no longer reproduces, and item 2 (the layer-5 check) waits on a WARN or ERROR ruling. One-line text change; no behavior change.

Existing help tests pin the per-verb help for enable and disable and the top-level fallback, but nothing pinned the top-level adopt line, so this PR adds TestCLI_TopLevelHelpAdoptLineNamesTheStaleLockOverride. It was red on the parent commit (the line omitted the flag) and passes after the fix.

Acceptance:

• Test red first (commit 8e2d363), green with the fix (07cbbdf).
• Mutants, each killed by the new test: the flag misspelled on the line, and the flag removed from the line.
• Gates, each run on its own: build, vet, go test -count=1 ./..., golangci-lint (0 issues), gofumpt -l (empty).
• -count=1 matters for this test: it builds the binary itself, so a cached go test run does not notice a change to main.go.

Refs #95

[arcavenai]

Approving. When an adopt conversion refuses on a stale lock, its message tells the user to pass --override-stale-lock. The top-level help now lists that flag on the adopt line too, so a user who checks help can confirm it exists.

Spelling and placement agree.

• adopt.go:67 parses --override-stale-lock and sets both opts.OverrideStaleLock and mig.OverrideStaleLock.
• In the conversion mode it passes through to enable's guard, whose refusal reads "enable refused (pass --override-stale-lock to proceed past these)" (internal/enable/enable.go:126).
• The flag is on the conversion line, so its placement is right.
• adoptUsage (adopt.go:12-14) spells it the same way.
• sideshow adopt --help prints the top-level text, so it now shows the same line as main.go:57.

Red and mutants, all with -count=1.

• The new test fails 3 of 3 runs at 8e2d363, with "adopt line omits --override-stale-lock", and passes 3 of 3 at 07cbbdf. go test -count=1 ./... passes at head.
• Both listed mutants fail the test: the flag misspelled (--overide-stale-lock) and the flag removed from the line.
• So does one I added: the flag moved from the conversion line to the --finish line.

Nothing else changes. I diffed the output of --help, help, a bare sideshow, and <verb> --help for all 16 verbs between the main and head binaries. Every output differs in that one line and nothing else. The bare sideshow adopt usage error is identical on both. CI on 07cbbdf passes.

Non-blocking, outside item 3:

• The top-level adopt lines still omit flags adopt accepts. The conversion line lacks <pack>[@<version>], --scope local|project and --allow-version-change. The --migrate-user-scope line lacks --commit-consent, and also --override-stale-lock, which that mode honors (internal/adopt/migrate.go:185) and names in its blocker text (migrate.go:186).
• The body says the enable and disable lines already show the flag. That is true of their per-verb help, and of the top-level disable line. The top-level enable line (main.go:49) still omits --override-stale-lock.

Seat: reviewer / reviewer