fix: improve reset command messaging to reduce user anxiety

[robotdad]

Summary

User feedback indicated the amplifier reset command feels "scary" - people worry about losing their session transcripts.

Changes

New "other" category for uncategorized files

• Files in ~/.amplifier/ not covered by known categories (projects, settings, keys, cache, registry) are now captured in an "other" category
• "other" is preserved by default, so user experiments and custom configs won't be silently deleted
• The list of files in "other" is shown dynamically so users see exactly what's being preserved

Improved messaging throughout

Help text:

• Leads with "Safe by default" messaging instead of examples
• Shows [preserved by default] next to safe categories
• Reorders examples: safe operations first, dangerous last
• "nuclear option" → "use with caution"

Execution output:

• Adds upfront reassurance: "Your session transcripts are safe - projects/ will be preserved."
• "Remove" → "Clean parts of" for consistency with step 1 ("Clean UV cache")
• "Install" → "Reinstall" to clarify it's refreshing, not starting fresh

Interactive UI:

• Adds reassurance at top: "Your transcripts and settings are preserved by default. Only cache/registry are removed (they auto-regenerate)."

Before/After

Help text before:

Reset Amplifier installation with category-based preservation.
...
Examples:
  amplifier reset --full -y            Remove everything (nuclear option)

Help text after:

Reinstall Amplifier while preserving your data.

Safe by default: Your session transcripts, settings, API keys, and any
custom files are preserved. Only the cache and registry are cleared
(they auto-regenerate on next run).
...
Examples:
  amplifier reset                      Interactive mode (recommended)
  amplifier reset -y                   Quick reset with safe defaults

Dry-run output after:

Your session transcripts are safe - projects/ will be preserved.

Reset Plan:
  1. Clean UV cache
  2. Uninstall amplifier (if installed)
  3. Clean parts of /home/user/.amplifier
       Preserving: keys, other (commands, team-tracking.yaml), projects, settings
       Removing: cache, registry
  4. Reinstall amplifier from: git+https://github.com/microsoft/amplifier

Testing

Tested in shadow environment - all messaging changes verified working.