pgxp: emit hook macros + dual build targets + flavor-namespaced caches (phase 2)

Emitter side of the value-propagation engine (ENHANCEMENTS.md G1.10):

- recompiler/src/pgxp_hook_emitter.{h,cpp} (new, in the codegen-hash
  surface): ONE hook grammar shared by BOTH emitters, wrapping loads/
  stores/COP2 transfers and precision-carrying ALU ops (moves, add/sub,
  or-merge, shifts, LUI, HI/LO, muldiv) with PGXP_*() macros. Clobberable
  sources are captured into locals before the statement. Precision-
  destroying ops (AND/XOR/SLT/...) are deliberately unhooked - validate-
  on-read drops their stale shadows for free.
- code_generator.cpp: central append in translate_instruction; LWC2/SWC2
  emissions capture the RAW loaded/stored word (a masked GTE register
  write must validate against the word as loaded).
- strict_translator.cpp: translate() wraps translate_impl()'s c_code with
  the shared grammar; deferred load-delay variants hook the psx_ldd temp.
- BIOS regenerated, fingerprints verified CHANGED (SCPH1001 + OpenBIOS;
  42.6k/12.2k macro sites). Base runtime + 33/33 tests green against it.
- Gating: macros expand only under -DPSX_PGXP=1. runtime.cmake grows a
  PGXP option on psxrecomp_add_runtime_target (defines PSX_PGXP=1 +
  PSX_OVERLAY_FLAVOR=2, _pgxp exe suffix) and PSX_PGXP_VARIANT to build
  the sibling target from the same generated tree (framework runtime +
  game wrapper). No ABI version bump needed: the appended PGXPHooks
  table is NULL-tolerant and the flavor half of the ABI tag rejects any
  host/DLL flavor mix.
- Shard caches: flavor folded into the cache tag (cg<V>_<hash>_gc<hash>
  _f<flavor>) in overlay_loader.c + compile_overlays.py so base and pgxp
  caches never share a directory; compile_overlays.py passes
  -DPSX_PGXP=1 when flavor bit 2 is set; overlay preamble forwards
  psx_pgxp_* through the table. PSX_OVERLAY_CODEGEN_VER 9 -> 10.
- Env overrides PSX_GEOMETRY_CORRECTION / PSX_PERSPECTIVE_TEXTURING /
  PSX_PGXP_CPU_MODE (validation path: free-running headless boots arm
  from the first vertex); census grew produced/swc2_stores and the pgxp
  verb reports suppress/active gate state.

Validated: PSXRecomp_pgxp.exe boots the recompiled BIOS with hooks armed
(engine active, per-vertex lookups flowing; the BIOS shell has no RTPS
content so produced=0 there is correct - coverage measurement moves to a
3D title in phase 3).

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

runtime/src/main.cpp

@@ -12123,6 +12123,16 @@ session_reboot:
     /* Sub-pixel vertex precision + perspective-correct UVs. Both default off;
      * with both off every setter below leaves the tracking caches disabled and
      * the draw path is the faithful integer one, unchanged. */
+    /* Env overrides (debug/validation path, like PSX_BIOS_HLE): arm the
+     * corrections from process start so free-running (headless) boots can be
+     * measured from the first projected vertex — a TCP toggle always arrives
+     * after the interesting window. '0' = off, anything else = on. */
+    if (const char* e = std::getenv("PSX_GEOMETRY_CORRECTION"))
+        g_video_geometry_correction = (*e && *e != '0') ? 1 : 0;
+    if (const char* e = std::getenv("PSX_PERSPECTIVE_TEXTURING"))
+        g_video_perspective_texturing = (*e && *e != '0') ? 1 : 0;
+    if (const char* e = std::getenv("PSX_PGXP_CPU_MODE"))
+        g_video_pgxp_cpu_mode = (*e && *e != '0') ? 1 : 0;
     gte_geometry_correction_set(g_video_geometry_correction);
     gpu_texture_correction_set(g_video_perspective_texturing);
     pgxp_set_cpu_mode(g_video_pgxp_cpu_mode);