chore(release): refresh README and CHANGELOG for 1.0.0-rc.1

[davydog187]

Update README and CHANGELOG for 1.0.0-rc.1

Plan: .agents/plans/A12-readme-changelog.md
Closes #173

The VM rewrite (Luerl → Elixir-native) is significant enough to warrant a major version bump rather than a minor. This PR retargets from 0.5.0 to 1.0.0-rc.1 — pre-release leaves room to catch regressions before locking 1.0 final while still signaling the magnitude of the change.

Goal

Refresh user-facing docs to reflect the new VM and bump the version to 1.0.0-rc.1.

Success criteria

• README.md accurately describes the new VM (no Luerl claims in Features/encoding tables; only a historical mention in Credits).
• CHANGELOG.md has a 1.0.0-rc.1 section summarizing:
  • VM rewrite (Luerl → Elixir-native)
  • Performance improvements (PRs feat: benchmark against Luerl and C Lua #143, perf: right-size register tuple allocations #153–perf: fully tail-recursive CPS executor with line tracking off heap #156)
  • Lua 5.3 suite pass rate (5/29 files)
  • Behavioral differences from 0.4 (encoded value tags, parser error format, integer wrapping, MFA encoding removed)
  • Bug fixes referenced by PR/issue
• mix.exs @version bumped to 1.0.0-rc.1.
• Doctests in lib/lua.ex still pass (52 doctests, 0 failures).
• mix docs does not introduce new warnings (the 6 warnings present are pre-existing on main and reference hidden modules — out of scope; noted in Discoveries).

Changes

 .agents/plans/A12-readme-changelog.md | 65 ++++++++++++++++++++++++++++--
 .agents/plans/A13-release-rc1.md      | 38 ++++++++++--------
 CHANGELOG.md                          | 85 ++++++++++++++++++++++++++++++++++-
 README.md                             | 60 +++++++++++++++-----------
 ROADMAP.md                            | 22 ++++++----
 mix.exs                               |  2 +-
 6 files changed, 222 insertions(+), 50 deletions(-)

README revisions:

• Tagline rewritten: "ergonomic interface to Luerl" → "Elixir-native Lua 5.3 virtual machine".
• Features list updated to describe the new VM and its capabilities.
• Encoding/decoding table replaced :luerl.tref()/:luerl.usdref()/:luerl.erl_func() with the new VM's tags ({:tref, integer()}, {:udref, integer()}, {:native_func, fun}). Removed the MFA row since the new VM doesn't accept that form.
• Credits section reframed: still acknowledges Luerl as prior art, but no longer claims this library "piggy-backs off" Luerl.

CHANGELOG 1.0.0-rc.1 entry covers Added / Changed / Removed / Performance / Fixed buckets, with PR references for all major fixes shipped under Direction A.

ROADMAP and plan A13 retargeted to 1.0.0 milestone naming. ROADMAP's stale 4/24 suite count corrected to 5/29.

Discoveries

• Version: framing this as 0.5.0 undersold the magnitude of the VM rewrite. After discussion the version was bumped to 1.0.0-rc.1.
• mix docs emits 6 pre-existing warnings on main (references to hidden modules Lua.CompilerException, Lua.Compiler.Scope.State). These are about code visibility, not docs content — out of scope for a README/CHANGELOG plan. This PR does not introduce new warnings.
• ROADMAP said 4/24 suite files passing; the actual count is 5/29 (bitwise.lua was added as ready in fix(vm): handle Lua 5.3 hex and string coercion for bitwise ops #198/feat(stdlib): implement math.fmod for bitwise.lua bit32 verification #199). ROADMAP updated.
• The {module(), atom(), list()} MFA encoding form is no longer accepted by Lua.encode!/2 in the new VM. Documented in the CHANGELOG's Removed section.

Verification

mix format         # no diff
mix compile --warnings-as-errors   # ✓
mix test           # 52 doctests, 45 properties, 1420 tests, 0 failures, 31 skipped
mix docs           # 6 pre-existing warnings (same as main); no new warnings

Out of scope (intentional)

• Tagging and publishing to Hex — that's plan A13 (Cut 1.0.0-rc.1).
• Migration guides — there are no breaking public-API changes from 0.4. The breaking changes are in encoded value tag shapes and parser error strings, both noted in Changed.
• Fixing the pre-existing mix docs warnings about hidden modules.