Achievement browser: clamp Stats scroll to content, drain queued key repeats

[stphung]

Fixes the two bugs reported against the redesigned achievement screen.

Bug 1 — Stats tab scrolls into the void

On the summary (Stats) tab, holding Down ran the scroll offset far past the content: the view stopped moving, but every subsequent Up had to unwind the invisible excess before anything scrolled back. Root cause: the input layer allows up to 100 scroll steps (it can't know the viewport), while the renderer clamped only what it drew and threw the clamp away.

Fix: render_stats_view now returns the offset it actually rendered — clamped so the last content line stops at the bottom of the viewport — and the browser persists it (render_achievement_browser takes &mut state). The first Up always moves immediately, and on a terminal tall enough to show everything the offset clamps to zero. The same fix reaches the character-select splash browser, whose Stats tab previously could not scroll at all (its Down handler passed the empty Stats category's count of 0).

Bug 2 — held arrow keeps scrolling after release

Keyboard auto-repeat (~25–30 events/s) outran the game loop, which deliberately processed one key event per ~100ms frame in normal mode — so a held arrow built a backlog that kept replaying after the key was released.

Fix: the event loop now drains everything already queued before drawing each frame (matching what realtime-minigame mode always did), bounded at 32 events per frame so pasted input can't starve the tick loop. Non-press events no longer end the drain early.

Verification

• New regression test stats_overscroll_is_clamped_back_by_the_renderer pins the clamp: overshoot clamps back, one Up moves from the clamp, re-render is a fixed point, tall-terminal clamps to zero.
• Live drive-game verification: a 30-Down burst on the Stats tab settles the instant it stops (two captures 1.5s apart identical); one Up scrolls immediately from the clamp; the splash Stats tab scrolls.
• All snapshots byte-identical (45 UI + 35 overlay); full make check green (fmt, clippy, 2908 lib + all integration tests incl. QUEST_ACT2=1 flag_on, progression check, voyage gate, audit).

🤖 Generated with Claude Code

https://claude.ai/code/session_011F9nMko3AYUQBsrCtPjBKp

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