Fold gc --all into --cache all

[janicduplessis]

Closes #143.

Description

--all named a scope but set a depth. It meant "empty the cache whole rather than trim it by age", and it reached caches only, never devices or project entries. Beside --cache, which does name a scope, the two read as if they contradict each other:

gc --delete --all --cache "compilation cache"

Solution

--cache carries the scope, with all as the reserved name for every cache:

gc --delete --cache all                   empty every cache whole
gc --delete --cache "compilation cache"   empty the matching caches whole
gc --delete --cache all --older-than 30   trim those entries by age
gc --delete                               caches untouched

Emptying whole is what --cache does, since that is what naming a cache asks for, and --older-than still asks for trimming. all is matched before the substring search, so a declared cache directory carrying install cannot answer to --cache all.

collectGcReport derives "empty whole" from the same rule the CLI uses, so the internal API cannot disagree with the flags.

Behavior change

gc --delete --all emptied every cache and reaped devices, dead project entries and stale locks. gc --delete --cache all empties caches and inspects nothing else; the reaping stays with bare gc --delete. Running both is two commands now, and each does one thing.

This split is what keeps the compilation-cache remedy safe: a user recovering a broken build runs gc --delete --cache "compilation cache", and that must not also delete their simulators.

One flag combination also inverts. gc --delete --all --older-than 30 emptied, because the old --all branch ran ahead of the trim branch. gc --delete --cache all --older-than 30 trims, which is what asking for an age filter should mean.

A bare gc --delete still leaves every cache alone, which is the property that separates the safe tier from the destructive one in skill/SKILL.md and docs/field-test-protocol.md.

Risk

--all is removed rather than deprecated, so a script carrying it now fails with unknown option '--all' instead of doing something different quietly. The CLI is pre-1.0 and the flag is documented only in this repo.

Test plan

• gc --cache all reports every cache and states that devices and project entries were not inspected
• gc --all exits with unknown option '--all'
• gc alone still reports without touching caches
• selectCaches covers all, its case-insensitivity, and a /opt/install/cache directory that must not answer to it
• guide cleanup and guide settings print --cache all, and the guide contract test now fails if a retired flag reappears in any topic (verified by reintroducing the old text)