sljit: refresh stale docs/comments + ISSUES #7

Documentation only. Prior sessions kept re-deriving state from breadcrumbs that
were no longer true:
- overlay_sljit.c / code_provider.{h,c}: corrected "declines every fragment" and
  "compile_fragment not yet called from dispatch" — the MIPS->sljit emitter is
  fully implemented and wired (then validated via the same-state diff).
- ISSUES.md: add Issue #7 (sljit live execution was unvalidated; the pure-live
  save-load wedge), root cause and fix recorded.

(SLJIT.md — the §11 forward plan and architecture clarification — lives at the
workspace root F:/Projects/psxrecomp/SLJIT.md, outside this repo, updated
separately.)

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

runtime/include/code_provider.h

@@ -15,8 +15,9 @@
  *     rescan on the emu thread. Seconds of latency; many fragments per run.
  *   - SYNC / ON-MISS (compile_fragment): the sljit model. JIT a single fragment
  *     in-process at a dispatch miss, sub-ms, return a native fn the caller
- *     registers immediately. (Wired into the dispatch path in SLJIT.md step 5;
- *     defined here so the abstraction is honest about both modes, not gcc-only.)
+ *     registers immediately. Wired into the dispatch path (overlay_loader.c
+ *     try_sljit_region); the sljit shard is then VALIDATED via the same-state
+ *     diff before it runs live (see SLJIT.md §11 / overlay_loader_dispatch).
  *
  * A provider sets the hooks it supports and leaves the rest NULL; callers
  * null-check before invoking. The gcc provider's batch hooks are thin pass-