fix(coding-agent): only report packages as up to date when pi update checked them (#11711)

## Problem

#11707 prints `Packages are already up to date` whenever no package
changed. In two cases that claim is false.

**1. npm left the old version installed.** Extension updates install
`@latest` or the configured range. If npm resolves stale registry
metadata, it reinstalls the old version and exits 0. The existing check
warns, then the summary contradicts it:

```
Updating npm:foo...
npm:foo is still 1.2.0 (registry reports 1.3.0); npm registry metadata may be stale, try again in a few minutes
Packages are already up to date
```

**2. Offline mode.** With `--offline` or `PI_OFFLINE=1`,
`updateConfiguredSources()` returns before checking anything, and the
CLI still prints `Packages are already up to date`.

## Change

The CLI only prints "already up to date" when the update ran and printed
no warning:

| Situation | Output |
|---|---|
| Packages changed | `Updated N packages:` and the list (unchanged) |
| Nothing changed, no warnings | `Packages are already up to date`
(unchanged) |
| Nothing changed, a warning was printed | `No packages were updated,
see the warnings above` (or `<source> was not updated, ...`) |
| Offline mode | `Skipped package updates (offline mode)` |

The CLI counts `progress` update events, which are always warnings, and
does not try to map them to packages. That is deliberate: the git
warning about untracked files that could not be cleaned is printed even
though the commit did change, so a warning does not mean "this package
was not updated".

In offline mode, `update()` still runs, so `pi update <unknown source>`
still fails with "No matching package". `isOfflineModeEnabled()` is now
exported from `core/package-manager.ts` (not from the package index) so
the CLI uses the same check.

The changelog entry from #11707 is adjusted, since it is unreleased.

## Tests

`test/package-command-paths.test.ts`, both through `main()`:

- npm `view` reports 1.3.0 but `install` leaves 1.2.0: the
stale-metadata warning is printed, then `No packages were updated, see
the warnings above`, and no "up to date".
- `PI_OFFLINE=1`: `Skipped package updates (offline mode)`, no "up to
date".

Both fail without the fix. `cycles project package overrides in config
local mode`, `prints a pnpm metadata hint when self-update fails` and
`should expand ~ in exclusion and exact patterns` fail locally on
Windows, on `origin/main` as well.

packages/coding-agent/CHANGELOG.md

@@ -4,7 +4,7 @@
 
 ### Added
 
-- `pi update` now lists each updated package with its npm version or git commit change, for example `npm:foo 1.2.0 -> 1.3.0`, and prints `Packages are already up to date` when nothing changed. `PackageManager.update()` reports each changed package as a new `result` progress event whose `message` holds that line ([#11707](https://github.com/earendil-works/pi/pull/11707))
+- `pi update` now lists each updated package with its npm version or git commit change, for example `npm:foo 1.2.0 -> 1.3.0`, and prints `Packages are already up to date` when nothing changed. When nothing changed but an update printed a warning, for example because npm left the old version installed after resolving stale registry metadata, it prints `No packages were updated, see the warnings above` instead; in offline mode it prints `Skipped package updates (offline mode)`. `PackageManager.update()` reports each changed package as a new `result` progress event whose `message` holds that line ([#11707](https://github.com/earendil-works/pi/pull/11707), [#11711](https://github.com/earendil-works/pi/pull/11711))
 
 ## [1.5.0] - 2026-11-02