feat(upgrade): add -Syu upgrade for tofu-installed recipe packages
- src/tofu/commands/upgrade.d: full 7-step upgrade pipeline
- Fetches index, lists installed state, compares versions
- Shows upgrade plan with confirmation prompt
- REUSES installCommand per outdated package (force=true, noconfirm=true)
- Continue-on-failure for multi-package upgrades
- Binary-only packages excluded (pool=binary → skip)
- 6 unittests: no-installed, all-uptodate, outdated-upgraded,
removed-from-index, multi-with-failure, confirmation-denied
- src/main.d: wire upgrade stub → upgradeCommand(pa, cfg)
- Evidence: dub test (23/23 pass) + dub build clean
huntedbytheirs
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