feat: disambiguate same-named monitors with relative position labels

[utahcon]

Summary

Fixes #81.

When two or more monitors are the same model, the indicator menu shows identical names for all of them, so there is no way to tell which layout row belongs to which monitor. This PR appends a relative position label to the name of any monitor that shares its name with another one, e.g.:

• DELL U2723QE (left) / DELL U2723QE (right)
• LG HDR 4K (top) / LG HDR 4K (bottom)
• ASUS PB278 (top left) / ASUS PB278 (top right) / ASUS PB278 (bottom)

Monitors with unique names are left untouched, so nothing changes for setups that aren't affected by the problem.

Why position labels instead of number suffixes

The discussion in #81 originally converged on appending the monitor's number (e.g. LG Electronics 34" 1, LG Electronics 34" 2). This PR instead implements the relative position labels later suggested by @rloutrel in that thread, for the reason @GuillaumeAmat reported: monitor numbers get reassigned interchangeably every time a monitor is (un)plugged, so a number suffix doesn't reliably tell the user which physical screen a row refers to, while "left"/"right" does. Numbers are still used as a tie-breaker when positions can't disambiguate (e.g. mirrored displays get middle 1 / middle 2).

How it works

• New src/indicator/monitorNames.ts exposes disambiguateMonitorNames(), which groups monitors by name and computes a position label only for groups with duplicates.
• Positions are derived by clustering monitor center points into columns and rows. The clustering tolerance is half of the smallest monitor dimension in the group (with a fallback when geometry is unavailable), so slightly misaligned monitors still land in the same row/column.
• Labels are picked from the cluster ranks: left/middle/right horizontally and top/middle/bottom vertically, combined when the group spans both axes (e.g. top right).
• If two monitors in a group would still get the same label (mirrored displays, or 4-in-a-row where two are middle), the labels are numbered (middle 1, middle 2) so every entry stays unambiguous.
• Whole phrases are passed through _() rather than composing translated words, since word order differs between languages.
• Both name sources go through the same disambiguation: the GNOME 49+ Meta.Monitor.get_display_name() path and the gjs subprocess fallback used on older shells.

Since MetaLogicalMonitor exposes no geometry properties to GJS (only get_monitors() and get_number()), the GNOME 49+ path now reads x/y/width/height from the shell's monitors matched by monitor index instead of the previous (logicalMonitor as any).x access, which silently yielded 0 for every monitor. Related: #142 describes row-to-monitor confusion of a similar nature, though on an older code path — this PR does not claim to fix it.

Test plan

• npm run lint passes and npm run build succeeds
• Also verified against the v18.0 branch: no conflicts, the two files touched here lint clean, and the build succeeds — happy to retarget there if you prefer
• Tested locally on GNOME 50 (Fedora) with same-model monitors: each menu entry shows the monitor name with its position label appended
• Test on GNOME shell <= 44 (subprocess fallback path — logic is shared, but I couldn't exercise it locally; happy to get help here per CONTRIBUTING.md)
• Test vertical and 2x2 arrangements on real hardware