Fleet UI: Add copy for policy tied to install software

[RachelElysia]

Issue

For #25245 (Addition to #22813)

Description

• Adds help text sentence to policy that has install_software key
• Links to software details page, tooltip
• Shorten other help text according to Figma
• Change Targets to Target

Note

API doesn't return extension like shown in figma design so UI does not show extension on the software name

Screenshot

Checklist for submitter

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

• Manual QA for all new/changed functionality

[iansltx]

Technically we only show the --- for failed policies (/cc @noahtalerman), so if the software got installed on the host some other way the policy will show as passing, but as long as we're aware of that nuance internally proceeding with this copy seems fine.

Thanks for the quick turn on this change!

[codecov]

Codecov Report

Attention: Patch coverage is 75.00000% with 2 lines in your changes missing coverage. Please review.

Project coverage is 63.85%. Comparing base (e956220) to head (f5c4d5b).
Report is 3 commits behind head on main.

Files with missing lines	Patch %	Lines
...d/components/PlatformSelector/PlatformSelector.tsx	85.71%	1 Missing ⚠️
frontend/hooks/usePlatformSelector.tsx	0.00%	1 Missing ⚠️

Additional details and impacted files

@@           Coverage Diff           @@
##             main   #25242   +/-   ##
=======================================
  Coverage   63.85%   63.85%           
=======================================
  Files        1616     1616           
  Lines      153833   153840    +7     
  Branches     3975     4027   +52     
=======================================
+ Hits        98224    98232    +8     
+ Misses      47796    47795    -1     
  Partials     7813     7813           

Flag	Coverage Δ
frontend	53.26% <75.00%> (+0.03%)	⬆️

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