feat(aircraft): hover-select, follow-on-select, richer sidebar, stable list, configurable area/refresh

[Kohei-Wada]

Builds on the OpenSky auth work (#393) with a batch of aircraft UX, plus one reusable engine primitive.

New primitive

• map:project(lon, lat) -> col, row | nil (MapApi::project) — exposes the world→terminal-cell projection so plugins can hit-test the mouse cursor against their own markers in screen space. Unit-tested.

Aircraft

• Follow-on-select (the headline): changing the selection — keyboard C-n/C-p, Enter, or hover — now anim.fly_tos the selected aircraft, so the map follows the list like the wiki plugin. Previously only Enter moved the map.
• Hover-select: moving the mouse onto (~2 cells of) a marker selects that aircraft. Movement-gated (keyboard selection still works while the mouse is parked) and pan-stable (compares projected cells, not lon/lat).
• Stable list + pinned selection: the sidebar is sorted by icao24 so rows keep their place across refreshes instead of reshuffling every fetch, and the selection is re-pinned to the same physical plane (by icao) after each refresh rather than a bare index.
• Richer sidebar: shows ground speed (km/h) and climb/descent (↑/↓) alongside altitude; also parses origin_country / squawk.
• Auth-aware refresh: opensky.interval_sec() = 5 s authenticated (matches OpenSky's 5 s resolution) / 12 s anonymous, overridable via ttymap.aircraft.interval_sec.
• Configurable fetch area: ttymap.aircraft.bbox_half_deg (default 5° → 10°×10°) — the bbox, not max_count, is what bounds how many aircraft are returned; widen it (at higher credit cost) to see more.

Verification

• luac -p on all touched Lua; unit test for map:project (on-screen → cell, off-canvas → nil).
• cargo test (full workspace), clippy --all-targets, fmt --check pass.
• Not exercised in CI: the live interactive behaviour (hover, fly, OpenSky round-trip) — needs a real TTY + credentials; verified manually against a live OpenSky account.

Follow-ups (not in this PR)

• Country flags in the sidebar (needs a name→ISO2 table; terminal flag-emoji rendering varies).
• Possibly restrict hover to highlight-only if follow-on-hover proves too aggressive.

[amazon-q-developer]

This PR successfully implements hover-select, follow-on-select, stable list sorting, richer sidebar displays, and configurable refresh intervals for the aircraft plugin. The code quality is high with comprehensive unit tests covering the new map:project() API and proper error handling throughout.

Key Changes Verified:

• New map:project() primitive correctly projects world coordinates to terminal cells with proper bounds checking
• Hover-select uses Chebyshev distance for hit detection with movement gating to avoid conflicts with keyboard navigation
• Stable list sorting by icao24 prevents UI churn across refreshes
• Selection pinning ensures the highlighted aircraft stays consistent after data refreshes
• Auth-aware refresh intervals (5s authenticated, 12s anonymous) with configuration override support
• Enhanced sidebar displays velocity (km/h), vertical rate (↑/↓), and maintains ground state indicators

Testing:

• Unit tests verify map:project() correctly handles on-screen and off-canvas coordinates
• All existing tests pass (cargo test, clippy, fmt)
• Manual verification confirmed with live OpenSky account (as noted in PR description)

The implementation is merge-ready with no blocking defects identified.

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