More options for positioning/anchor, opacity, name max length

[francislavoie]

Followup on #240, closes #67 (anchoring)

• Opacity by default changes the opacity of the entire user row including the avatar, but I want it to only affect the background behind the username (I want avatars to always be fully opaque), so I added a "target" option.
• Opacity is now a slider instead (easier to use).
• Add anchor horizontal and vertical options, where horizontal maps to the existing option in the nav-bar of switching left/center/right side (but now also reflected in the config, and synced if either changes), and vertical anchor so there's now the option of having it grow upwards. If "center" is chosen for horizontal then top/bottom is ignored (I don't have a usecase for that mode so I don't know how best to integrate that if at all).
• The anchor horizontal option is now persisted and loaded properly, previously it would need to be toggled each time if you want it on the left when you open the app, pretty annoying.
• Added a Max username length limit which truncates the usernames with a ... if too long. This makes sure the overlay will be limited on width, better to plan consistent layouts if using this with OBS for streaming. I realize resizing the window also does this to a certain extent, but I think having both is good for level of control.
• Added a Scale option, between 50% and 200%. This gives really nice control, and doing it in-app instead of in OBS after the fact or w/e means it'll render very crisp.

In a followup commit:

• Cleaned up the nav-bar buttons to use the 👆 cursor
• Added a pin/unpin toggle button on the settings window's General page
• Made the settings window start opened but minimized, made the X button not close but minimize; this gives easier access to toggling unpin (on first-time-use of the app, it's surprising and confusing if you pin and then realize "oh shit how do I unpin aaaaaaaaaa", so I think this is a better default). Users can find the settings pane via their taskbar (on Windows anyway, I don't know if this behaves weird on Mac/Linux)
• Removed 1px pin border from the settings window (it should only affect the overlay, not also the settings window)
• Made it save the overlay position/size settings immediately after change, instead of only on quit, because when dev-ing I noticed if I Ctrl+C kill it, the overlay position didn't persist. Thought that was weird.

Disclosure: I largely used Github Copilot to write the code changes, but I manually tested and made many minor adjustments by hand afterwards.

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