feat(tui): queue strip — always-visible queued prompts, ^Q controls

[jkyberneees]

Round-2 follow-on: the always-visible queue panel (A10 continued past the visibility-only increment in #42).

What it does

• One row per queued prompt, always visible directly above the input — held prompts were invisible between submit and drain.
• ^Q focus mode: ↑↓/jk select · ←→/hl move · d delete · esc/⏎ back to the composer. Only latches when prompts are queued; drops focus automatically when the queue drains.
• ▲ ▼ ✕ per-row mouse controls: reorder, delete, or click a row body to select it.
• Overflow tail past 8 rows (names the hidden selection while focused); cancel returns held prompts to the input for editing (existing behavior, now strip-aware).

Correctness details

• Mouse controls render only with --mouse — glyphs without terminal mouse tracking are dead pixels; mouseless runs get a ^q manage hint row that becomes the key legend while focused.
• Hit-testing in terminal cells, not byte offsets — multibyte prompt text (emoji/CJK) shifted every byte-based hit zone by 2 cells per glyph, so ▼ moved up and ✕ moved down. Both the dispatcher and the test helper now compute display-width columns; covered with ASCII and multibyte prompts.
• Layout math stays tri-party consistent: View, inputAreaHeight, and mouse offsets all derive from queueStripHeight.
• F1 help card teaches ^Q; README synced.

Verification

• go test -race -count=1 ./... — all 7 packages ok (~38s tui)
• go vet clean, go fmt clean
• New tests: cell-accurate clicks (▲▼✕ incl. clamped edge), hidden-controls-without-mouse, hint-row inertness, F1 coverage, plain-mode parity, focus latch/unlatch, overflow windowing