style(icons): use filled variants for user, comment, share, password

[pringelmann]

• Resolves: Use filled icons in the part of Activity activity#2662

Summary

Activity's navigation mixed filled and outline icons. The outline ones are shared core assets, so this swaps four of them for the filled Material Symbols variants. The .png siblings go along since they're used for activity emails.

These assets also show up in notifications and settings sections, so it changes them there too.

Before	After

Checklist

• Code is properly formatted
• Sign-off message is added to all commits
• Tests (unit, integration, api and/or acceptance) are included
• Screenshots before/after for front-end changes
• Documentation (manuals or wiki) has been updated or is not required
• Backports requested where applicable (ex: critical bugfixes)
• Labels added where applicable (ex: bug/enhancement, 3. to review, feature component)
• Milestone added for target branch/version (ex: 32.x for stable32)

AI (if applicable)

• The content of this PR was partly or fully generated using AI

[jancborchardt]

We should use outlined icons here everywhere in the nav, except for the active entry which should be filled.

Yes indeed, really sorry for the lack of detail on the issue

[pringelmann]

Actually the original issue seems wrong? nextcloud/activity#2662 FYI @artonge

We should use outlined icons here everywhere in the nav, except for the active entry which should be filled. Sorry for the confusion @pringelmann

Ah I see, no worries will fix

[pringelmann]

@jancborchardt one trade-off worth flagging: in order to switch out active & inactive icon states we will have to create and maintain an icon map. This will only reference core filters/apps. We could extend it to include specific 3rd party apps, but there is a risk that they become stale if the app ever changes its icon.

Another issue is that some app icons like Deck don't have MDI equivalents, so we'd have to either ship the app icon with activity, or use a different icon.

Without 3rd-party mapping	With 3rd-party mapping: (custom Deck icon)