Clarify "Not supported" on Hosts page by adding tooltip (#49301)

<!-- Add the related story/sub-task/bug number, like Resolves #123, or
remove if NA -->
**Related issue:** Resolves #39987

- Added tooltips to the "Agent," "Last restarted," and "Status" column
headers on the Hosts page explaining which platforms are supported and
why.
- On the Host details page, vitals with a "Not supported" value are now
hidden instead of shown.
- Fixed the "Last restarted" vital showing on ChromeOS hosts, where it's
not actually collected.
- Updated the "Last opened" tooltip on the Host details Software table
to explain why it's only supported for native macOS, Windows, and Linux
apps and packages.
- Remove cellProps.rows.length === 1 workaround (which suppresses the
tooltip whenever the table has exactly one row) by adding the correct
CSS which removes the tooltip overflowing if host table is only 1 row

# Checklist for submitter

If some of the following don't apply, delete the relevant line.

- [x] Changes file added for user-visible changes in `changes/`,
`orbit/changes/` or `ee/fleetd-chrome/changes`.
See [Changes
files](https://github.com/fleetdm/fleet/blob/main/docs/Contributing/guides/committing-changes.md#changes-files)
for more information.

## Testing

- [x] Added/updated automated tests
- [x] QA'd all new/changed functionality manually

<!-- This is an auto-generated comment: release notes by coderabbit.ai
-->
## Summary by CodeRabbit

- **New Features**
- Added/updated explanatory tooltips for Hosts table column headers
(Agent, Last restarted, Status) with clearer supported-platform wording.
- Clarified “Last opened” tooltip scope to native macOS, Windows, and
Linux app/package entries.

- **Bug Fixes**
- Removed “Last restarted” from Host details for ChromeOS hosts when the
value isn’t collected.
- Prevented vitals rows from rendering when their values resolve to “Not
supported,” and tightened “Last restarted” platform visibility.
- Fixed tooltip overflow/positioning in the single-row Host software
table case.

- **Tests**
- Updated and expanded vitals/header coverage to match the new display
rules.
<!-- end of auto-generated comment: release notes by coderabbit.ai -->

changes/39987-clarify-not-supported-tooltips

@@ -0,0 +1,4 @@
+- Added tooltips to the "Agent", "Last restarted", and "Status" column headers on the Hosts page explaining which platforms are supported and why.
+- Fixed the "Last restarted" vital showing on ChromeOS hosts, where it's not actually collected.
+- Updated the "Last opened" tooltip on the Host details Software table to explain why it's only supported for native macOS, Windows, and Linux apps and packages.
+- Removed the `cellProps.rows.length === 1` workaround (which suppressed the tooltip whenever the table had exactly one row) by adding the correct CSS, which removes the tooltip overflowing if the host table is only 1 row.