v1.0.0

Description

• Implemented a full tree-walking interpreter (engine/interpreter/): Value/Environment
  model, Python-style function-level scoping with explicit change x to global bridging,
  1-based indexing/slicing with negative-index support, collections (add/remove/replace/
  indexed change, insertion-ordered maps), functions (returnable/async in any
  combination), or_else error recovery, and use/from/DLC:* module loading.

• Implemented CuffScript's custom pattern-matching engine from scratch (engine/regex/):
  a dedicated compiler + backtracking matcher for the full docs/REGEX.md dialect
  (character classes, presets, [one:...], named/numbered captures, quantifiers including
  N~M ranges and lazy variants, anchors, flags), wired into is/IS, match ... from,
  find ... from, replace ... in ... to, split ... by, and count ... in — including a
  step-count + time-limit safety guard against catastrophic backtracking.

• Introduced a systematic, extensible error hierarchy (engine/common/ErrorCodes.h,
  engine/common/CuffError.h): every error carries a stable numeric code, category,
  location, message, and optional hint, and is marked recoverable/non-recoverable so
  or_else catches exactly the right things.

• ./cuffc program.cuff now runs the program by default; --ast reproduces the previous
  tokens/AST-dump behavior for engine development.

• Fixed several defects that prevented the previously-committed engine from compiling or
  running at all (broken relative includes, a use-before-complete-type cycle between the
  statement/expression sub-parsers, a real dangling-copy bug in await parsing, a missing
  -Wunused-variable), added single-quoted string literals (needed for map/match key access
  inside f-strings per docs/REGEX.md), fixed f-string {{/}} escaping and nested-brace
  handling, and corrected ! to bind looser than comparison (!lvl is MAX_LEVEL now means
  !(lvl is MAX_LEVEL), matching the spec's own examples).

• Added docs/IMPLEMENTATION_NOTES.md documenting every place the language spec leaves
  runtime behavior unspecified and the choice this engine makes there (async model, DLC
  function list, module-merge semantics, etc.), and docs/EXTENDING.md as a guide for
  adding new builtins/DLC libraries/statements/expressions.