v0.2.6 - UTF-8 + bash brace fix for non-ASCII pass-phrases

Fixed — non-ASCII pass-phrase regression (reported via #2)

• UTF-8 round-trip in JSON helpers. scripts/common.sh json_emit_context
  and json_get layered :encoding(UTF-8) on both STDIN and STDOUT around
  Perl's JSON::PP, which already emits UTF-8 byte sequences from
  encode_json. Every byte was re-interpreted as Latin-1 and re-encoded —
  e.g. e5 8f a3 (口) became c3 a5 c2 8f c2 a3 mojibake. The hook output
  was invalid UTF-8, Claude Code rejected it with the cryptic
  "UserPromptSubmit hook error: Failed with non-blocking status code: No
  stderr output", and the matching handoff was already consumed by
  rm -f $f → silent data loss for users with Chinese/emoji prompts.
  Fix: keep binmode STDIN only on json_emit_context (decode bytes →
  wide chars before encode_json sees them) and only binmode STDOUT on
  json_get (decode_json wants raw bytes). Verified end-to-end with
  继续 ZZZ and 测试 中文 emoji 🎉 round-trips.
• Bash variable-name lexer eats high-bit bytes after $slot. Found
  while debugging the UTF-8 bug. The context template 已粘贴口令续接 handoff $slot。
  put the Chinese full stop 。 (U+3002 = e3 80 82) immediately after a
  bare $slot. Bash's identifier lexer absorbed the high-bit bytes as if
  they were valid identifier chars, expanded ${slot。} (unset under
  set -u) → exit 1 → handoff already deleted by line 63 → silent loss.
  The outer } 2>/dev/null || exit 0 wrapper swallowed the actual
  unbound variable: slot� diagnostic. Fix: brace-quote every
  ${slot} / ${trimmed} / ${body} reference in the context templates.
  Pure-ASCII users were never affected (no high-bit bytes after the
  variable = no absorption).

Compatibility

• Pure-ASCII pass-phrases (continue A, next A, drop A) behaved
  identically before and after these fixes — anyone unaffected by the
  Chinese-byte bugs sees no behavior change. Upgrading is recommended for
  any user who has ever pasted a Chinese pass-phrase, since the silent
  data-loss path can consume a handoff without injecting it.