fix(cli): render scannable QR on Apple Terminal with full-cell ANSI

[okaynaffo]

Closes #133.

Apple Terminal adds inter-line spacing and uses fonts that distort half-block glyph QRs (qrcode-terminal small:true with those block characters), so the mobile app could not scan the code.

Changes:

• New packages/crosscode/src/qr.ts renders each module as a full terminal cell with explicit ANSI black/white backgrounds, EC M and 4-module quiet zone by default. No half-block glyphs, theme independent.
• printTunnelQr keeps its provider signature and now supports --no-qr (URL only) and --small-qr / CROSSCODE_QR_SMALL=1 (compact full-cell, margin 2 + EC L).
• Swaps qrcode-terminal for maintained qrcode (already used by web).
• Docs (docs/cli.md) and changeset included.

Verified:

• pnpm --filter crosscode build passes, tsc --noEmit clean.
• Render check: 45-module payload yields 53 rows with margin 4, ANSI cells present, zero half-block chars; small mode 41 modules yields 45 rows.
• node dist/cli.js help shows new flags; bundle no longer contains qrcode-terminal.

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[okaynaffo]

Superseded: force-push with corrected commit author did not sync to this PR. Opening a fresh PR from the corrected branch.